Uncooled infrared sensor

ABSTRACT

An uncooled infrared sensor can be used for a plurality of applications such as fire fighting, surveilling a border or any desired area, and limb sounding. The uncooled infrared sensor includes manually or automatically adjustable optics that receive an electromagnetic signal, focus the electromagnetic signal and provide a focused electromagnetic signal to a focal plane array. The focal plane array includes a plurality of detector devices disposed in rows and columns to form the focal plane array. Each detector device is constructed so as to have a reduced pitch and provide a maximum number of detectors within a minimum square area of the focal plane array. Each detector device detects the focused electromagnetic signal incident upon it, converts the focused electromagnetic signal into a sensed signal and outputs the sensed signal so that the focal plane array provides a plurality of sensed signals. The sensor also includes a focal plane array processor that has a plurality of cells corresponding to the plurality of detector devices. The focal plane array processor receives the plurality of sensed signals, processes the plurality of sensed signals to correct for any gain and any offset errors between the plurality of sensed signals due to any inconsistencies between any of the detector devices of the focal plane array and any inconsistencies within the cells of the focal plane array processor itself, and outputs a plurality of processed signals. The sensor also includes a display processor that receives the plurality of processed signals and converts the plurality of processed signals into a video signal suitable for display. The focal plane array processor, the display processor and a controller also provide temperature stabilization of the sensor, manual or automatic calibration of the sensor, manual or automatic gain and level control of the sensor and automatic or manual calibration of the sensor.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §120 as acontinuation of co-pending U.S. non-provisional application Ser. No.11/211,149, filed Aug. 24, 2005, which is a continuation of U.S.non-provisional application Ser. No. 11/010,826, filed Dec. 13, 2004,which is a continuation of U.S. non-provisional application Ser. No.10/787,836, filed Feb. 25, 2004, which is a continuation of Ser. No.10/444,500, filed May 23, 2003, which is a continuation of Ser. No.10/254,444, filed Sep. 25, 2002, entitled UNCOOLED INFRARED SENSOR,which is a continuation of Ser. No. 10/036,098, filed Nov. 9, 2001,entitled UNCOOLED INFRARED SENSOR, which is a continuation of Ser. No.09/797,424, filed Mar. 1, 2001, entitled UNCOOLED INFRARED SENSOR, whichis a continuation of Ser. No. 09/584,939, filed Jun. 1, 2000, entitledUNCOOLED INFRARED SENSOR, which is a continuation of Ser. No.09/434,893, filed Nov. 5, 1999, entitled UNCOOLED INFRARED SENSOR, whichis a continuation of Ser. No. 09/291,836 filed Apr. 14, 1999, entitledUNCOOLED INFRARED SENSOR, which is a continuation of Ser. No. 09/162,977filed Sep. 29, 1998, entitled UNCOOLED INFRARED SENSOR, which is acontinuation of Ser. No. 08/994,247 filed Dec. 19, 1997, entitledUNCOOLED INFRARED SENSOR, which in turn is a continuation-in-part (CIP)of the following U.S. non-provisional applications or patents:

Ser. No. 08/751,516 filed Nov. 15, 1996, entitled A DUAL-BANDMULTI-LEVEL MICROBRIDGE DETECTOR, now U.S. Pat. No. 5,811,815;

Ser. No. 08/760,240, filed Dec. 4, 1996, entitled INFRARED RADIATIONDETECTOR HAVING A REDUCED ACTIVE AREA, now U.S. Pat. No. 5,760,398;

Ser. No. 08/547,344, filed Oct. 24, 1995 entitled UNCOOLED FOCAL PLANEARRAY SENSOR;

Ser. No. 08/574,815, filed Dec. 19, 1995, entitled METHOD AND APPARATUSFOR THERMAL GRADIENT STABILIZATION OF MICROBOLOMETER FOCAL PLANE ARRAYS,now U.S. Pat. No. 5,763,885;

Ser. No. 08/921,725, filed Aug. 27, 1997, entitled MONOLITHICANALOG-TO-DIGITAL CONVERTER;

Ser. No. 08/914,703, filed Aug. 19, 1997, entitled DIGITAL OFFSETCONVERTER; and

Ser. No. 08/919,889, filed Aug. 28, 1997, entitled BOLOMETRIC FOCALPLANE ARRAY.

This application also claims the benefit under 35 U.S.C. §120 of each ofthe following U.S. Non-Provisional Applications, as at least one of theabove-identified U.S. Non-provisional Applications similarly is entitledto the benefit of at least one of the following Non-provisionalApplications:

Ser. No. 08/450,339, filed May 25, 1995, entitled MONOLITHICANALOG-TO-DIGITAL CONVERTER;

Ser. No. 08/496,026, filed Jun. 28, 1995, entitled DIGITAL OFFSETCONVERTER; and

Ser. No. 08/521,266, filed Aug. 30, 1995, entitled BOLOMETRIC FOCALPLANE ARRAY.

Each of the foregoing applications or patents is hereby incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to uncooled infrared sensors, and inparticular, the invention relates to various features and applicationsof an infrared uncooled sensor.

2. Discussion of the Related Art

A radiation detector is a device that produces an output signal which isa function of an amount of radiation that is incident upon an activeregion of the radiation detector. Infrared detectors are those radiationdetectors which are sensitive to radiation in the infrared region of theelectromagnetic spectrum. An infrared detector may be, for example, athermal detector. A thermal detector detects radiation based upon achange in the temperature of an active region of the detector due toabsorption of the radiation to be detected.

Thermal imaging sensors having a plurality of thermal detectors thatdetect a representation of an object by the objects' thermal emissions.In particular, energy emitted by an object is dependent on numerousquantities such as, for example, the emissitivity and the temperature ofthe object. Infrared thermal sensors typically detect one or both ofthese quantities and use the detected information to produce an imagecapable of being visualized by a user of the sensor.

Infrared detectors may be classified as, for example, either cryogenic(typically liquid nitrogen temperatures) or uncooled detectors.Cryogenic infrared detectors are typically made of small band gap (about0.1-0.2 eV) semiconductors such as HgCdTe and operate as photo diodes orphoto-capacitors by photon absorption to produce electron-hole pairs. Incontrast, uncooled infrared detectors do not make use of the small bandgap semiconductor device because the band gap is too small at, forexample, room temperature such that any signal swamps the detector.Consequently uncooled infrared detectors may be less sensitive thancryogenic detectors but do not require a cooling apparatus or itsassociated energy consumption. For portable, low-power applicationswhere the sensitivity of cryogenic detectors is not needed, thepreferred choice is an uncooled thermal detector. A thermal detector maybe any of three types typically: a pyroelectric detector, a thermocoupleor a bolometer.

An array of bolometer detector devices may be formed integrally with anintegrated circuit. The integrated circuit may be used to processelectrical signals produced by the array of bolometers in response tothe infrared energy impinging on the array of bolometers. In such anarray, each of the bolometers includes an infrared energy receivingsurface which is made of a material that has its resistivity change asits temperature changes, in response to the infrared energy impinging onand being absorbed by the material. Thus as the bolometer absorbsradiation, both its temperature and electrical resistance change. Ameasure of radiation absorbed by a bolometer can be made by measuringchanges in its electrical resistance. For example, by placing thebolometer in series with a voltage supply, the current in the bolometerwill vary in accordance with the infrared energy sensed by thebolometer. An electronic read-out circuit connected to the voltagesupply and serially connected to the bolometer may be used to produce anoutput signal representative of the infrared energy impinging on thematerial. An array of such bolometers will produce a plurality of outputelectrical signals that may be fed to a processor and used to providethe electronic image of the source of the infrared energy.

Such infrared sensors have numerous applications such as missileguidance, thermal imaging, target acquisition, target tracking and lawenforcement surveillance. Several prior art references disclose infraredimaging systems, methods, and arrays that make up such infrared sensors.The present invention is an improvement to an uncooled infrared imagingsensor.

SUMMARY OF THE INVENTION

An embodiment of an infrared sensor of the present invention includes anoptical element that receives an electromagnetic signal, focuses theelectromagnetic signal and provides a focused electromagnetic signal toa focal plane array. The focal plane array of the sensor includes aplurality of detector devices disposed in columns and rows to form thefocal plane array. Each detector within the focal plane array detectsthe focused electromagnetic signal incident upon the detector device,converts the focused electromagnetic signal into a sensed signal andoutputs the sensed signal so that the focal plane array provides aplurality of sensed signals at an output of the focal plane array. Thesensor also includes a focal plane array processor having a plurality ofcells associated with corresponding detector devices of the focal planearray. The focal plane array processor receives the plurality of sensedsignals, processes the plurality of sensed signals to correct any gainand any offset errors between each of the plurality of sensed signalsdue to any inconsistencies between each of the detector devices and thecells of the focal plane array processor, and provides a plurality ofcorrected signals at an output of the focal plane array processor. Thesensor further includes a display processor that receives the pluralityof corrected signals and converts the plurality of corrected signalsinto a video signal suitable for output to a display.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and features of the present invention will become apparentfrom the following detailed description when taken in connection withthe following drawings. It is to be understood that the drawings are forthe purpose of illustration only and are not intended as a definition ofthe limits of the invention.

FIG. 1 is a schematic block diagram of an embodiment of an uncooledinfrared (IR) sensor according to the present invention;

Table 1 identifies a plurality of manually adjustable lenses, motorizedlenses, or athermalized lenses that may be used with the uncooledinfrared sensor of the present invention;

FIG. 2 illustrates a schematic diagram of an embodiment of a focal planearray (FPA) of the uncooled IR sensor of the present invention,including circuitry for accessing rows and columns of the FPA;

FIG. 3 illustrates a block diagram of an embodiment of an FPA assemblyof the uncooled IR sensor of the present invention;

FIG. 4 illustrates a schematic block diagram of an embodiment of adisplay processor of the uncooled IR sensor of the present invention;

FIG. 5 illustrates an embodiment of a control panel of a controller ofthe uncooled IR sensor of the present invention;

FIG. 6 illustrates a schematic block diagram of an embodiment of anequalization controller of the display processor of FIG. 4;

FIG. 7 illustrates a histogram plot provided by the equalizationcontroller of FIG. 6;

FIG. 8 illustrates a plot of a transfer function provided by theequalization controller of FIG. 6;

FIG. 9 illustrates a gain and level curve provided by the equalizationcontroller of FIG. 6;

FIG. 10 illustrates an embodiment of the FPA of the uncooled IR sensorof the present invention;

FIG. 11 illustrates an embodiment of masking the FPA of the uncooled IRsensor of the present invention;

FIG. 12 is a side elevation view of an embodiment of a detector deviceof the uncooled IR sensor of the present invention;

FIG. 13 is a side elevation view of another embodiment of a detectordevice of the uncooled IR sensor of the present invention;

FIG. 14 is top plan view of the detector device of FIG. 13;

FIGS. 15( a), 15(b) and 15(c) illustrate three respective embodiments ofconductive legs of the detector device of FIGS. 12-14, and some masklayers used to fabricate the respective embodiments;

FIG. 16 illustrates some steps for forming the embodiment of conductivelegs of the detector device as illustrated in FIG. 15( a);

FIG. 17 illustrates some steps for forming the leg structure of thedetector device as illustrated in FIG. 15( b);

FIG. 18 illustrates some steps for forming the leg structure of thedetector device as illustrated in FIG. 15( c);

FIG. 19 is a side elevation view of layers used to form the detectordevice of FIGS. 13-14;

FIG. 20 is a photo of the detector device of FIG. 12;

FIG. 21 illustrates a cross-sectional side elevation view of an invertedmesa point (MP) contact via hole according to an embodiment of thedetector device of FIG. 12;

FIG. 22 illustrates steps for forming the detector device of FIG. 12with the inverted MP contact of FIG. 21;

FIG. 23 illustrates an embodiment of the FPA of the uncooled IR sensorof the present invention, having a plurality of detector devices thatshare a single contact between the plurality of detector devices;

FIG. 24 illustrates another embodiment of the FPA of the uncooled IRsensor of the present invention, having a folded leg design for each ofthe detectors devices;

FIG. 25 is a plot of an absorptance versus a wavelength of operation ofa plurality of embodiments of the detector device of the uncooled IRsensor of the present invention;

FIGS. 26( a), 26(b) and 26(c) illustrate, respectively, a helmetmounted, a goggle mounted configuration and an enlarged view of a headmounted embodiment of the uncooled IR sensor of the present invention;

FIG. 27 illustrates a block diagram of the head mounted uncooled IRsensor of FIGS. 26( a), 26(b) and 26(c);

FIGS. 28( a), 28(b) and 28(c) illustrate another embodiment of theuncooled IR sensor of the present invention which is a hand-held sensor,wherein FIG. 28( a) illustrates a monocular sensor and FIGS. 28(b)-28(c) illustrate a binocular sensor;

FIGS. 29( a) and 29(b) illustrate another embodiment of the uncooled IRsensor of the present invention which is a weapon sight, in particular,FIG. 29( a) illustrates a top view of the weapon sight and FIG. 29( b)illustrates a block diagram of the weapon sight;

FIGS. 30( a) and 30(b) illustrate another embodiment of the uncooled IRsensor of the present invention which is a camera/recorder (camcorder),in particular FIG. 39( a) illustrates a cross-sectional view of thecamcorder and FIG. 30( b) illustrates a block is diagram of thecamcorder;

FIGS. 31( a) and 31(b) illustrate another embodiment of the uncooled IRsensor of the present invention which is a microscope, in particularFIG. 31( a) is a side elevational view of the microscope and FIG. 31( b)is an operational block diagram of the microscope;

FIGS. 32( a) and 32(b) illustrate another embodiment of the uncooled IRsensor of the present invention which is a radiometer/spectrometersystem, in particular FIG. 32( a) illustrates a cross-sectional view ofthe radiometer/spectrometer and FIG. 32( b) illustrates a block diagramof the radiometer/spectrometer;

FIG. 33 illustrates an embodiment of a border surveillance system of thepresent invention;

FIG. 34 illustrates an embodiment of the uncooled IR sensor that may beused in the border surveillance system of FIG. 33;

FIG. 35 illustrates the uncooled IR sensor of FIG. 34 as used in theborder surveillance system of FIG. 33;

FIG. 36 illustrates limb sounding with the uncooled IR sensor of thepresent invention; and

FIG. 37 illustrates an embodiment of the uncooled IR sensor that may beused to limb sound according to the present invention.

DETAILED DESCRIPTION

FIG. 1 illustrates a schematic block diagram of an embodiment of anuncooled infrared sensor according to the present invention. With theimaging system of FIG. 1, electromagnetic radiation such as, forexample, infrared radiation in a wavelength range of 8-14 μm may beincident upon optics 106, focussed by the optics such as, for example, alens to provide a focussed electromagnetic signal at output 107. Thefocussed electromagnetic signal is imaged onto an uncooled focal planearray (FPA) 102. The FPA converts the focussed electromagnetic signal toa plurality of sensed signals that are output on medium 109, to a focalplane array processor 108. The focal plane array processor 108 processesthe plurality of sensed signals such as, for example, by digitizing theplurality of sensed signals to provide a plurality of digital signalsand by adjusting the plurality of digital signals for any differences ingain or other non-uniformities between the plurality of detector devicesof the focal plane array to provide a plurality of processed signals.The plurality of processed signals are then output on medium 111 to adisplay processor 110. The display processor reformats the plurality ofprocessed signals into a plurality of display signals in a formatsuitable for display on display 112 such as, for example, NTSC, RS-170or PAL-B color video, and outputs the display signals to the display onmedium 113. As will be discussed in further detail infra, the displayprocessor may perform a plurality of functions such as, for example,reformatting for the display signals, calibrating the uncooled infraredsensor, eliminating bad pixel data, manual or auto focus adjustment,addition of symbols and/or other information to the display signals,adjustment of brightness and/or contrast of the display signals, and thelike.

A controller 114 provides automatic and/or manual control of the displayprocessor 110 to allow automatic and/or manual adjustment of the variousdisplay parameters such as for example, the brightness, the contrast,adding symbols, and the like. Alternatively, a high speed parallel link(HSL) such as an IEEE 1284 connection 118 or a serial interface such asan RS-232 connection 105, can be coupled to a host computer 103 tocontrol the uncooled infrared sensor 104. The uncooled infrared sensoris powered, through power connector 103, by supply electronics 116 whichmay include any one of a battery, an AC power supply, or a DC powersupply 116.

The uncooled infrared sensor 104 of FIG. 1 generally provides a2-dimensional real-time display of an image for an operator of thesystem to view. For example, in a preferred embodiment of the uncooledIR system of the present invention, the FPA processor 108, includes anuncooled focal plane array 102 that, as will be discussed in more detailbelow, is configured to operate over at least one infrared (IR)wavelength band of interest. With this system, the operator can viewthermal signatures of objects and/or scenery under conditions where thehuman eye would not normally be able to see the objects and/or scenery.For example, the imaging system may be used at night, in the day withoutwashout conditions, in the presence of smoke, or in degraded weatherconditions and the like.

The uncooled infrared sensor of FIG. 1 may also include a shutter 101(shown in phantom). When the shutter is opened, incident IR energyimpinges upon the FPA 102 and when the shutter is closed, no incident IRenergy is allowed to impinge upon the FPA. The shutter may be controlledby a shutter controller (not illustrated) disposed within the displayprocessor 110 and controlled via a control signal on line 98. However,it is to be appreciated that the uncooled IR sensor need not include theshutter mechanism and may alternatively include, for example, anystandard hand adjustable, motorized or athermalized optics 106. Theadjustable optics 106 of the uncooled IR sensor may be manually orautomatically focused to either focus or defocus a scene to be viewed bythe uncooled IR sensor. A user can simply manually adjust the manualfocus of the optics, or the display processor may include an auto focusmechanism (not illustrated) to move the optics to focus and defocus thescene. As will be discussed in greater detail below, the displayprocessor may also include a panel of control buttons 96, wherein onecontrol button 97 may be used to control the focus mechanism of theoptics in the manual mode.

The optics 106 of the IR sensor 104 may be any of a plurality ofstandard optics that are hand-adjustable, motorized, or athermalized. Inparticular, Table I illustrates a plurality of manually adjustablelenses, motorized lenses or athermalized lenses having various apertures(mm/in), field of views (FOV), F/No.(H), EFL (mm). Any of these lensassemblies may be attached to the uncooled IR sensor.

As will be discussed in greater detail infra, the FPA 102 includes aplurality of detector devices that make up a plurality of pixel elementsof the FPA wherein each pixel element provides a signal representativeof an amount of energy incident upon the individual detector. It is tobe understood that for this specification a detector device is anydevice that includes a sensing element that provides an electricalsignal in response to a sensed signal such as, for example, anelectromagnetic signal by the sensing element. The detector device canbe, for example, a bolometer detector, a photon detector, aferroelectric detector, a diode detector, and the like. It is also to beunderstood that the sensing element may measure any physical parametersuch as, for example, temperature, stress, signal amplitude, signalfrequency, and the like. As will be discussed in greater detail infra,in one embodiment of the uncooled infrared sensor of the presentinvention, the FPA may comprise an array of microbridge bolometerdetectors organized in rows and columns, having over 80,000 individualbolometer detectors.

As is illustrated in FIG. 2 the FPA 102 may be arranged in a grid ofdetectors including a plurality of columns (C₁, C₂, C₃, C₄, C₅, C₆, C₇ .. . ) and a plurality of rows (R₁, R₂, R₃, R₄, R₅ . . . ) wherein theindividual detectors may be addressed using a row select register 94 andcolumn circuitry 92. The column circuitry may address any column withinthe array and the row select registers may address any row within thearray so that access may be had to any detector within the array. InFIG. 2, each individual detector provides a sensed signal that iscoupled to the column circuitry, wherein each column is accessible bythe associated column circuitry and each detector within each column isselected by the row select register. However it is to be appreciatedthat the circuitry may be provided so that each row of detectors providea sensed signal that is coupled to row circuitry, wherein the rowcircuitry is substantially the same as the column circuitry above, andeach detector may be selected with a column by a column select registerthat is substantially identical to the row select register discussedabove. As will be discussed in greater detail below, a preferredembodiment of the FPA comprises a plurality of microbridge bolometerdetectors.

FIG. 3 illustrates a block diagram of a focal plane array package 90,that includes the combination of the FPA 102 and the FPA processor 108(see FIG. 1). The FPA receives IR signals through an IR window 88. TheIR window may be made of a material transparent to the IR operating bandsuch as, for example, germanium (GE) or the shutter 101 may replace theIR window. The FPA provides a detected signal for each detector withinthe FPA. The signal output by each detector within the FPA is typicallysmall so that amplification of the signal is required. The read-outintegrated circuit (ROIC) 15 houses the FPA and provides circuitry toamplify the detected signals, into amplified signals, a plurality ofanalog-to-digital converters (A/D) to convert the amplified signals todigital signals and circuitry to subtract an offset from each of thedigital signals to correct for any non-uniformities that exist betweeneach of the detectors, amplifiers, and A/D converters. As will bediscussed in greater detail below, the offset value is provided by thedisplay processor 110 on line 86. However, it is to be appreciated thatthe offset value may also be provided by the FPA processor and suchmodification is intended. The offset value is provided by the ROIC to doa course data substraction to offset any manufacturing inconsistenciesand thereby allows the analog-to-digital converter to be only 14-bits ofresolution. In contrast, if no offset correction were provided, then atleast 20-bit resolution A/D converters may be required. As will bediscussed in detail infra, the offset data is stored in memory in thedisplay processor. However, it is to be appreciated that this offsetdata may also be stored in memory in the FPA processor and that suchmodification is intended.

The FPA package 90 also includes a temperature stabilizer 84 that iscoupled to the ROIC 15. The temperature stabilizer has an input coupledto a temperature control signal 82 output by the display processor 110,which adjusts the average temperature of the ROIC and the FPA inresponse to the temperature control signal. The FPA package may alsoinclude a heat sink 78, and a cold shield or a shroud 76 which can beused to stabilize the temperature of the FPA package and, as will bediscussed in greater detail below, to eliminate any local radiation frominterfering with operation of the FPA assembly. In one embodiment of theuncooled IR sensor of the present invention, the temperature stabilizermay be a Thermoelectric (TE) cooler. The ROIC may include a temperaturesensor such as, for example, a diode (not illustrated) on the ROIC whichsenses the temperature of the ROIC and outputs a temperature sensesignal 80. The digitized temperature sense signal and the temperaturecontrol signal are communicated to the power supply module 116 (seeFIG. 1) over the power supply connector 103. The FPA package outputs thetemperature sense signal to the display processor which includes atemperature A/D converter 81 (see FIG. 4) for digitizing the temperaturesense signal. The power supply module includes a high current bridge andfilter for driving the TE cooler; these also form part a closedtemperature control loop. The temperature control loop provides the TEcooler drive signal to the FPA package through the display processor. Itis to be appreciated that although the bridge and filter have beenillustrated as being within the power supply module, they may alsoreside within, for example, within the display processor and that suchmodification is intended. With this arrangement, the temperature of theROIC and the FPA can be stabilized by adjusting the temperature with thetemperature stabilizer. One method and apparatus for stabilizing thetemperature of the FPA and the ROIC may include reading of thetemperature from the ROIC in the FPA package; providing the temperaturesense signal that is proportional to the temperature of the ROIC;generating the temperature control signal proportional to a desiredtemperature of the FPA and the ROIC with the TE driver; and stabilizingthe temperature of the ROIC and the FPA by adjusting the temperature ofthe ROIC with the temperature stabilizer.

One problem with an uncooled IR sensor 104 such as illustrated in FIG.1, is that it typically responds to all radiation incident upon the FPA102, including radiation from its immediate surroundings. However, thepredominant IR radiation entering the uncooled infrared sensor comesfrom the immediate surroundings and not from the scene that the uncooledIR sensor is focused upon. Because the uncooled IR sensor is sensitiveto the radiation from its immediate surroundings, it may be that achange in the ambient temperature of the uncooled IR sensor may resultin a loss of operating dynamic range of the IR sensor. For example, achange in the ambient operating temperature of the IR sensor may resultin a reduced operating range of the IR sensor due to the local radiationswamping out any signals from the scene of interest. For example, a+/−20° ambient temperature change may be the entire ambient operatingtemperature dynamic range over which the IR sensor can operate.Accordingly, there is a need to compensate the uncooled IR sensor forvarying ambient temperature changes to improve the operating dynamicrange of the uncooled IR sensor.

One way to compensate for changes in the ambient temperature is to usethe temperature compensation loop circuitry, including the TE cooler 84discussed above. In particular, the ambient temperature at the ROIC 15and the FPA 102 can be measured as discussed above; this assumes thatthe ROIC and the FPA package are at the ambient temperature. With thistemperature compensating loop circuitry, the ROIC and the FPA can becompensated for any change in the ambient operating temperature of theuncooled IR sensor. In one embodiment of the invention, this open loopcircuitry adjusts the ROIC and the FPA temperature approximately 1° forevery 50° in ambient temperature change. In other words, if the ambienttemperature goes up by, for example 100°, the ROIC and the FPA arelowered by 2° in temperature. Alternatively, if the ambient temperaturefalls by, for example, 50° then the ROIC and the FPA are increased byapproximately 1° in temperature. Thus, the temperature compensating loopcircuitry looks at the ambient temperature of the ROIC and the FPA anddecides in which direction and by how much to adjust the temperature ofthe ROIC and the FPA for the changes in the ambient operatingtemperature of the uncooled IR sensor.

Another way in which to control the temperature of the FPA 102 and theROIC 15 to help mitigate any effects of changes in the ambient operatingtemperature of the uncooled IR sensor 104 is to control the temperatureof the shroud or cold shield 76 around the FPA assembly 90. Referring toFIGS. 1 and 3, the shroud or cold shield may be placed, for example,around the optics 106 and, if provided the shutter 101, and enclose theFPA assembly 90 so as to shield the FPA and the ROIC from any radiationother than the radiation from the scene in the field of view of theoptics. The cold shield or shroud blocks any radiation from theimmediate surroundings of the FPA and the ROIC and the unoccupied spacewithin the FPA assembly can be pumped out and sealed to eliminate anyfurther local source of radiation. In addition, the cold shield orshroud can be temperature controlled via the above-described temperaturecompensating loop to stabilize its temperature in an environment wherethe ambient operating temperature may change. This will result in theFPA and the ROIC seeing a constant temperature from the immediatesurroundings and will increase the dynamic operating range andsensitivity of the uncooled IR sensor. For example, if the uncooled IRsensor only operates over the +/−20° dynamic range of ambienttemperature described above, then with either of methods and apparatusdiscussed above, the dynamic operating range may be increased to, forexample +/−60° in ambient operating temperature.

Still another way to control the temperature of the FPA 102 and the ROIC15 for any changes in the operating ambient temperature of the uncooledIR sensor 104, may be to adjust either of the detector bias voltage orthe detector bias current. Typically, each of the detectors in the FPAis biased with a bias current and a bias voltage. By changing either oneof or both of these values, in response to a sensed temperature changewith the above-described temperature compensating loop, each individualdetector can be compensated for the change in operating temperature.This may require a calibration of the circuitry for each sensor withinthe FPA, but, as will be described in detail infra, the uncooled IRsensor has the capability to perform a calibration of each detectorwithin the FPA. Thus, the calibration of each detector for changes inambient temperature of the uncooled infrared sensor can be incorporatedinto this calibration data.

Another embodiment of a temperature compensating loop of the presentinvention is a closed loop implementation where instead of measuring theambient temperature on, for example, the ROIC, the temperature of theFPA and the ROIC can be determined from the sensed signals output by theFPA and processed by the FPA processor 108 and the display processor110. Otherwise, the circuitry of the closed loop temperaturecompensating loop will be the same as discussed above with respect tothe open loop temperature compensating loop. The closed loop temperaturecompensating loop may comprise a signal averager coupled to thedigitized output signal from the FPA processor. The signal averager maydetermine an average signal representative of an average temperature ofthe FPA and provide this average signal on an output line. The averagesignal then may be used to control the temperature stabilizer in themanner discussed above. The closed loop implementation of thetemperature stabilizing loop may also be set so that a 50° change inambient temperature in one direction will result in a 1° change providedby the TE cooler to the ROIC and the FPA in an opposite direction. Oneadvantage of the closed loop implementation is that it exploits thetemperature sensitivity of the FPA, as opposed to a diode or othertemperature monitoring device disposed, for example, on the ROIC totemperature stabilize the FPA according to an average temperature ofeach of the detectors in the FPA.

As discussed above with respect to the open loop temperaturecompensating loop, the closed loop temperature compensating loop mayadjust the temperature of the FPA 102 and the ROIC 15 or may adjust thetemperature of the shroud or cold shield 76 surrounding the optics, theshutter and the FPA package, as discussed above. Alternatively, thisclosed loop temperature compensating loop may be used to vary one orboth of the detector bias voltage and the detector bias current tocontrol the operating point of each detector within the FPA.

It is to be appreciated that although it has been disclosed that ashroud or cold shield may be used to enclose the optics 106, the shuttermechanism 101 and the FPA assembly 90, that another manner for shieldingthe FPA 102 and the ROIC 15 from local radiation is to control thetemperature of the housing that surrounds the FPA assembly. Inparticular, instead of providing a shroud or cold shield, one can simplystabilize the temperature of the housing to the desired temperature andthus eliminate the need to provide an extra cold shield or shroud.

FIG. 4 illustrates a schematic block diagram of an embodiment of thedisplay processor 110 of the uncooled IR sensor of the invention. TheFPA processor outputs a digitized data signal on line 111 to the displayprocessor. (See FIG. 1). The display processor performs non-uniformitycorrection and defective pixel substitution processing on the digitizeddata. It was previously discussed above that coarse offset values areprovided on line 86 (see FIG. 1) by the display processor to the FPAprocessor to correct for any non-uniformities in the FPA 102 and theROIC 15. The display processor also includes a pixel (fine) offsetcorrector 48 that receives fine offset values on line 49 from an offsetmemory 50 and subtracts the fine offset values from the receiveddigitized data. Offset corrected data is then provided on line 51 to again controller 52. The gain controller receives gain correction valueson line 53 from a gain memory 54 and subtracts the gain correctionvalues from the offset corrected data to perform gain equalization onthe offset corrected data and provide gain corrected data on line 55.The gain correction data in gain RAM 54 is preprogrammed gain valuesstored in the gain memory to account for any manufacturing differences.The gain corrected data is provided to a pixel substitution controller56. The pixel substitution controller may correct the gain correcteddata for a defective pixel by averaging a plurality of pixels adjacentto the defective pixel and substituting an average value for thedefective pixel to yield corrected data on line 57. The pixelsubstitution controller may receive defective pixel information from thegain memory on line 59 that has been pre-programmed at the factory. Itis to be appreciated that any of the pixel offset corrector, the gaincontroller and the pixel substitution controller may be turned on oroff, for example, by a bit within a control word provided by hostcomputer 103 (see FIG. 1). As will be discussed in greater detail below,the corrected data may be supplied to an equalization controller 58 toconvert the corrected data to a format suitable for display. Inparticular, as will be discussed in detail infra, the equalizationcontrol loop may compute an intensity histogram and from this intensityhistogram determine a non-linear transfer function to be applied to thecorrected data to map the corrected data to, for example, an 8-bitdisplay format. As will be discussed below, this non-linear transferfunction is a variation of a technique known to one of skill in the artas plateau equalization.

It is to be appreciated that the offset memory 50 and the gain memory 54may be, for example, a random access memory (RAM). In one embodiment ofthe display processor 110 of the invention, the fine offset correctionvalues, the gain correction values and the defective pixel informationare initially stored in a non-volatile flash memory 60. The displayprocessor reads these values from the flash memory into either a fastDRAM or a fast SRAM that make up the offset memory and the gain memory.

The display formatted data is provided on line 61 to a videodigital-to-analog converter (DAC) 62 for generation of analog video datato be output by the display processor on line 113, for example, to thedisplay 112. In particular, the display processor may include a videoencoder (not illustrated) for generating a color composite video signalwith blanking and sync (CVBS) and separate video (S-video). The encodermay also be programmed to supply many different formats of video. In apreferred embodiment of the uncooled IR sensor of the invention, thedisplay processor 110 will output either NTSC, PAL-B, or RS-170,interlaced, square pixel video data. When composite color video isselected, for example, by a control word from the host computer 103 thedata is supplied, color coded as YCrCb, which contains luminescence (Y),chrome red (Cr), and chrome blue (Cb) data fields within the video data.The display processor may also provide a gray-scaled data by setting theinternal Cr and Cb gains to 0. This removes the color from the outputvideo data. It is to be appreciated that another way to provide thegray-scaled video data is to provide the Y (luminance-only) video outputof the encoder, which doesn't contain any color burst information. Whendigital video data is desired, the display processor may simply supplythe Y (luminance-only) data.

The gain correction, the offset correction, and the equalization controlmay all be automatically done. However, one advantage of the uncooled IRsensor 104 of the invention is that all these functions may also bemanually performed. For example, the uncooled IR sensor can be providedwith the control panel 96 having a plurality of control buttons thatallow manual adjustment of any of gain, the level, the calibration, theequalization, and the focus of the sensor. The controller 114 whichinterfaces to the display processor may also house the plurality ofcontrol buttons to manually control any of, for example, the gain, thelevel, the calibration, the equalization and the focus of the uncooledinfrared sensor.

FIG. 5 illustrates an example of a controller panel 96 that allows auser to manually control the uncool IR sensor 104. The controllerincludes a on/off switch 63 that allows power to be supplied to theuncooled infrared sensor; an auto-gain and auto-level button 64 (AGL)that evokes the automatic gain (contrast) and automatic level(brightness) implemented with the equalization controller 58, as will bediscussed in greater detail below; a calibration button 65 that allowsthe user to self-calibrate the uncooled infrared sensor; a focus rockerpanel 66 which allows the user to manually focus the motorized lens inthe optics 106; a manual gain knob 67 which allows the user to manuallyenter a gain amount to be applied to the video signal; and a manuallevel knob 68 which similarly allows the user to enter a manual levelvalue to the video signal. The AGL button issues a command to allow thecamera to automatically set the image contrast and the brightness levelson the display of the video signal. In contrast, the manual level buttonallows the user to vary the brightness level and the manual gain buttonallows the user to vary the contrast of the image. The uncooled infraredsensor may also be calibrated, for example, every ten minutes. However,by pressing the calibration button, the user can also perform a manualcalibration which will place the uncooled infrared camera into aninactive state for, in example, approximately one minute while thecalibration takes place.

One method for calibrating the uncooled infrared sensor 104, when theuncooled infrared sensor includes the shutter 101 (see FIG. 1) may be toclose the shutter so that the camera is looking at a uniform imageacross the FPA. All of the detectors of the FPA are assumed to be at thesame temperature such as, for example, approximately 300° K. Theresulting digitized video signal for each of the detectors or pixelsprovided by the display processor 110 can be stored in the offset memory50 (see FIG. 4) as the fine offset memory values. The fine offsetvalues, as discussed above, can be subtracted from the individualdetector signals when the camera focuses upon a scene. According toanother embodiment of the uncooled IR sensor of the invention, acalibration can be performed, for example, when the uncooled infraredsensor is not provided with a shutter mechanism by either automaticallyor manually defocusing the uncooled infrared sensor to defocus the sceneincident upon the FPA. The defocused scene then presents a more or lessuniform scene to each of the pixels of the FPA which can again beassumed to be approximately 300° K and can be used to perform thecalibration as discussed above. One advantage of using the non-focusedscene as the source of an image for the calibration is that the uncooledIR sensor can be provided without the shutter mechanism whichcontributes to the overall weight of the sensor. Thus, where theuncooled IR sensor weight is an issue, the sensor can be providedwithout a shutter mechanism and still be calibrated.

Referring again to FIGS. 1 and 4, the display processor 110 alsoincludes an FPA integration time controller 66 which allows theintegration time and the frame rate of the uncooled IR sensor 104 to bevariable and programmable. For example, the display processor can beprogrammed with control bits provided, for example, by the host computer103 (see FIG. 1) to control a horizontal sync pulse (HSYNC) provided bythe display processor to the FPA processor 108, which in turn, variesthe FPA integration time. For example, it may be desirable to operatethe uncooled infrared sensor at a frame rate of, for example, 60 Hz toupdate the display quickly for fast moving images or because theuncooled IR sensor itself may be moving. For such an application, aslower frame rate may not accommodate the dynamically changing videoinformation. In contrast, if the camera and the scene to be viewed arestatic, a slower frame rate and thus a longer integration time may beused. As discussed above, the signal from any detector within the FPA102 may be read out by corresponding column circuitry 96 and row selectregisters 94. The signal from each detector may be, for example,provided to an integration capacitor. The integration capacitorintegrates the signal output by the associated detector. The length oftime that the integration capacitor may integrate this signal can bevaried by circuitry such as disclosed in pending U.S. application Ser.No. 08/914,703, entitled Digital Offset Corrector, herein expresslyincorporated by reference. In particular, the integration time is theamount of time that the HSYNC pulse supplied by the display processor tothe FPA assembly is not asserted. Thus, the pulse width of the HSYNCpulse can be varied to accomplish this variable integration time. Anadvantage of this variable integration time is that the uncooledinfrared sensor can then be operated in greatly varying dynamic scenesor environments.

FIG. 6 illustrates a schematic block diagram of the equalizationcontroller 58 of FIG. 4. As discussed above, the equalization controllerprovides level control and gain control to the previously corrected dataon line 57 and transforms the previously corrected data into a word sizesuitable for display on the display 112 (See FIG. 1). It is to beunderstood that for the present invention “level control” is defined ascorrecting the digital video signal to set a mean value of the videosignal to a desired level such as, for example, a value of “0”. It is tobe understood that the level control and thus the mean value can beautomatically or manually adjusted, as discussed above, and that themean value can be any value and it is not intended to be limited to “0”.It is also to be understood that gain control is defined by the presentinvention as the mapping of an intensity of the pixel signal informationwith a certain gain factor to achieve an output quantized image that isconsistent with a word size format suitable to be displayed on thedisplay. In one embodiment of the equalization controller of the presentinvention the corrected data input signal is a 14-bit signal and anoutput of the equalization controller is compressed to an 8-bit signalsuitable for display. The uncooled IR sensor 104 of the inventionreceives energy with a very high dynamic range, and quantizes thereceived energy into corrected data from the FPA 102 at, for example, a14-bit quantization level. However, for a real-time display of such anIR image, the digital data may need to be mapped from its originalresolution to an 8-bit version for display. Thus, the equalizationcontroller acts to truncate the input signal and squeeze the inputsignal into an 8-bit display format.

As will be discussed in greater detail below, the equalizationcontroller 58 includes both histogram and plateau equalization so thatthe mapping of the original data is not linear. In particular, the skyor the ground are typically points of interest for a scene to be viewedby the uncooled IR sensor 104 of the invention. However, the data pointsin between may not necessarily be of interest. Therefore, it is ideal toapply a large gain to the points of interest and to apply very little orno gain to the areas that are not of interest, so that the areas ofinterest are displayed and the areas that are not of interest are not.Accordingly, it is desired to optimize the transfer function applied tothe video data to be output to the display. This is accomplished by theequalization controller of the present invention.

Referring to FIG. 6, the 14-bit digital corrected data on line 200 istruncated to 11-bits. The truncated 11-bit word is provided on line 202to a histogram generator 204. Referring to FIG. 7, the histogramgenerator provides on line 205, a plot of the number of pixels (on they-axis) at a plurality of intensity values (on the x-axis). An idealizedtransfer function discussed above would apply all of the gain to thepixels having the intensity value within the peak (P) of the curve asillustrated in FIG. 7, and little or no gain to the pixel values havingthe intensity outside of this peak. It is to be appreciated that thehistogram can be generated, for example, for one frame of the outputvideo signal, or for an average of several frames, as desired. Thehistogram data is then output to a low-pass filter 206. The low-passfilter smoothes out any fast moving images within the histogram data sothat a fast moving image does not swamp the equalized data output by theequalization controller. In other words, the low-pass filter smoothesensures that the histogram is applied over several frames of the data.

Typically, the histogram data on line 205 is integrated via theintegrator 208 illustrated in FIG. 6 to provide the transfer function tobe applied to the corrected data. However, one problem with histogramequalization is that the resulting gain applied to the corrected data isapplied mostly to the pixels in the main peak of the histogram and thereis little room remaining to apply any gain to any other pixels ofinterests. This tends to result in an unsatisfactory display, where thenoise in the vicinity of the histogram peak has been amplified at theexpense of, for example, information in parts of the remainder of thepicture with a typical levels. Accordingly, the present invention, priorto integrating the histogram data passes the histogram data on line 207to a plateau processor 212. The plateau processor clips the peak (P) andthe tails (T) of the histogram data as illustrated in FIG. 7. Byclipping the peak value to an arbitrary value, the plateau processeddata on line 209 may then be integrated with the integrator to output atransfer function illustrated in FIG. 8, that is de-emphasized withrespect to the pixels of interest. In addition, by clipping the tails ofthe histogram, the integrated data will provide a fixed gain to thesepixels. In other words, the clipped histogram data is fed to theintegrator and the integrator integrates the histogram to provide at anoutput a transfer function that is de-emphasized with respect to theclipped regions of the histogram data.

The integrated transfer function data on line 211 output from theintegrator has a slope and an offset value that may be stored in a slopetable 214 and an offset table 216 provided in memory. The corrected dataon line 201 output by the pixel substitution controller 56 (see FIG. 4)is multiplied with multiplier 216 by the slope of the gain of thetransfer function provided by the slope memory on line 213, to scale theintensity of the signal to be output by the equalization controller. Anoffset value on line 215 is added to the scaled signal on line 217 toset the mean value of the signal to be output to, for example, a valueof “0” as is illustrated in FIG. 9. The equalized signal on line 218will be, as discussed above, compressed in dynamic range or in otherwords, mapped to a format suitable for display on display 112. Asdiscussed above, if a composite color video is desired, chroma-red (Cr)and chroma-blue (Cb) data can be added to the corrected luminance only(Y) data output by the equalization controller on line 218.Alternatively, if digital video is desired or if gray-scale video isdesired, the Cr and Cb data need not be added to the corrected data. Asdiscussed above with respect to FIG. 3, the corrected video data is thensupplied to the video DAC 62 to provide the output video data.

It is to be appreciated that the histogram can be computed on any numberof pixels of the display that may be automatically selected or, selectedby the user such as, for example, by a control word provided by the hostcomputer 103 (see FIG. 1). It is also to be appreciated that althoughthe description has been with respect to computing a histogram andproviding plateau equalization to the histogram to yield a transferfunction to be applied to the corrected data, that any transfer functionmay be applied to the corrected data and that according the presentinvention, such transfer function may be programmed by the user. Thus,an advantage of the uncooled infrared sensor of the invention is that itprovides flexibility in the equalization control and transfer functionto be applied to the corrected data for display.

It is also to be appreciated that the above-described equalizationcontroller can be implemented in hardware, in software, or in acombination of both. For example, in one embodiment of the equalizationcontroller of the invention, a programmable logic device (PLD) may beused to implement the equalization controller. Alternatively, theequalization controller may be implemented for example, with a digitalsignal processor and appropriate software. In addition, as discussedabove, the equalization controller can be either automaticallycontrolled or user-controlled.

FIG. 10 illustrates a drawing of a portion of the FPA 102 of FIG. 1. TheFPA 102 comprises a plurality of detectors 10 as discussed above. In oneembodiment of the FPA 102 of the present invention, the FPA is organizedas a matrix of 246 rows of the detectors by 328 columns of the detectorsto yield over 80,000 individual detectors within the FPA. Referring toFIG. 1, the display processor 110 may process, for example, the center320×240 detector signals and supply coarse offset values on line 86 toeach of the 328×240 sensors. Referring to FIG. 2, each row (R₁, R₂, R₃,R₄, R₅ . . . ) in the FPA is addressed using a dynamic row selectregister 104 and each column (C₁, C₂, C₃, C₄, C₅, C₆, C₇) within the FPAis addressed using column circuitry 200 that addresses any particularcolumn. Thus the combination of the column circuitry and the row selectregisters allow any detector within the FPA to be addressed.

One problem with the FPA and associated circuitry as illustrated in FIG.2, is that noise exists and tends to be correlated between the columnsor rows. A user may see the correlated noise on the display and thiscorrelated noise may produce a distorted image to the user. For example,the user may see the correlated noise as horizontal lines for noisewithin a particular row or vertical stripes for noise within aparticular column. According to the present invention, one way toeliminate these correlated noise effects is to average the noise for aparticular row or column and to subtract the averaged value of the noisefor the particular row or column from the row or column.

Typically the noise drifts between the columns and rows and the amountof drift in the noise between a row and column are typically different.For example, each column circuit may behave a bit differently from theother column circuits to provide this correlated noise between thecolumns. The column correlated noise, can be subtracted out by simplyaveraging the detectors within a single column and subtracting theaverage of the noise from the detectors within a single column from eachdetector within a column. It is to be appreciated that this averagecomputation of the noise for each column does not need to occur forevery frame of the video signal, but that the substraction of theaverage noise value from each detector within the column should occurfor every frame of the video signal. However, it is also to beunderstood that the computation of the average noise for each column canoccur for every frame of the video signal and that such modification isintended.

For the rows within the FPA 102, the correlated noise between the rowstends to be the result of time varying issues. In particular, each rowwithin the array is sampled at a particular time and the noiseassociated with that row is correlated to the respective time value.Therefore, there may be more drift between the rows. According to theinvention, an average of the correlated noise for each row can bedetermined and subtracted from each detector within each row such asdescribed above for each column. Because the row correlated noise occurstypically more rapidly, this calculation should be done for each frameof the video signal and subtracted from each pixel within the row foreach frame.

One problem with subtracting the average signal from the row or columnis that using an average value of noise of a row or a column when thereis a hot spot in the row or column such as, for example, when there is ahot target in the row or column that will distort the averagecalculation and may actually exacerbate the noise problem that the eyetends to see on the display. The present invention solves this problemwith one embodiment by spatially masking the FPA 102 to provide a maskedarea 70 and an unmasked area, as illustrated in FIG. 11, and samplingpixels within either rows or columns or both of the spatially maskedarea of the focal plane array. The FPA has been spatially masked toprovide an area 71 that displays the scene and to provide an area 70that does not display the scene. Individual rows, columns, or pixelswithin each row or column can then be averaged within the masked areathat does not display the scene to determine an average correlated rowor column noise and this correlated row or column noise can besubtracted from each of the associated row and column pixels within thearea 71 that displays the scene.

In an alternate embodiment of the present invention, the individualdetectors within either or both of the rows and columns can be sampledduring a blanking interval where the signals from the individualdetectors are not used. For example, rows 243-246 and columns 1-328, canbe sampled during the blanking interval to determine an average row andcolumn correlated noise that can be subtracted from the detectors of theremainder of the FPA. With either of these embodiments, no signal fromany target is present within the signal used to determine the averagecorrelated noise and therefore no target will disturb the subtraction ofthe correlated noise.

It is to be appreciated that the spacial windowing of the FPA can beencompassed by any method known to those of skill in the art to limitthe field or view of the system such as, for example, by opening andclosing the shutter as discussed above, by zooming in and zooming outwith the adjustable optics, and by limiting the part of the focal planearray that is mapped to the display, as discussed above, to for example,a center 1/9th of the plurality of detectors. By limiting the field ofview or by “windowing of the array”, this portion of the array isessentially being blown up on the display and the remainder of the arrayis essentially not used. Therefore, the pixels within the rows andcolumns of the remaining array can be used to determine the average rowand column noise that can be subtracted from the portion of the arraythat is used to provide the image for the display.

FIG. 12 is a side elevation view of an embodiment of a detector device10 according to the present invention. This embodiment of the detectordevice 10 has an elevated microbridge detector level 11 and a lowerlevel 12. It is to be understood that for the present specification amicrobridge is any structure that is suspended above any surface. Thelower level 12 may include a semiconductor substrate 13 havingfabricated thereon components of the ROIC (See FIG. 2) 15. It is to beappreciated that numerous components such as for example diodes, FET's,bus lines, connections, contact pads, and the like can be fabricatedusing conventional fabrication technology and that such components areintended. For example, an electronic ROIC for a detector or an array ofdetectors such as disclosed in co-pending U.S. patent application Ser.No. 08/521,266 filed on Aug. 30, 1995, herein incorporated by reference,can be disposed in the semiconductor substrate 13 and is intended.

The components of the ROIC are coated with a protective layer ofsilicone nitride 16 which protects the ROIC from contamination. Theelevated microbridge detector level 11 includes a silicone nitride layer20, a resistive layer 21, a silicone nitride layer 22 disposed above thesilicone nitride layer 20 and the resistive layer 21, and an optional IRabsorbing layer 23 disposed over the silicone nitride layer 22.Downwardly extending silicone nitride layers 20′ and 22′, providesloping support walls for legs 38, 40 (not illustrated) that support theelevated microbridge detector level 11.

This embodiment also may include a thin film layer 18 of reflectivematerial deposited on the lower level 12, to provide a cavity 26 betweenthe elevated microbridge detector level 11 and the lower level 12. Avertical distance d, between the reflective layer 18 and the uppermicrobridge detector level 11, is chosen so that incident energy passingthrough layers 20, 21, 22 and 23 (if provided) is reflected by layer 18upwardly and has constructive interference properties with the IR energyinitially incident on the upper microbridge detector level 11. Inparticular, the distance d is chosen to be substantially a quarter of awavelength of a wavelength band of operation of the detector device, sothat a phase of the reflected energy is coincident with a phase of theincident IR energy on the upper microbridge detector level. Theresistive layer 21 and the optional IR absorbing layer 23 make up anactive area 32 (not illustrated) of the detector. The active areaabsorbs the incident IR radiation and converts the absorbed IR radiationinto heat. A resulting temperature change of the active area is sensedby measuring a change of resistance of the active area, which is afunction of the temperature change.

It is to be understood that for this specification the pixel collectingarea is defined as the area over which the detector device absorbsenergy that is incident onto the detector device. It is also to beunderstood that the active area 32 is defined as the total area thatincludes either one or both of an IR absorbing layer 23 and theresistive layer 21 that makeup the active area of the detector. Inaddition, it is to be understood that the pixel area or pitch is thearea containing the detector device, or in other words the area thatincludes either one or both of the upper microbridge level 11 and theROIC 15 on the lower level 12. It is further to be appreciated that thefill factor is a fraction of the pixel area that includes the activearea of the detector.

A sensitivity of the detector device 10 of FIG. 12 is a function of manyfactors including an absorption coefficient of each material making upthe active area 32 of the device over the desired wavelength band ofoperation, the physical structure of the detector including the cavitystructure 26, a thermal isolation of the active area provided by themicrobridge structure 11, and the like. For example, the cavity 26 andthe microbridge structure 11 provide thermal isolation of the activearea from its surrounding such as, for example, the ROIC 15 on thesubstrate 13, so as to obtain higher isolation than if the active areawere disposed on the top surface 14 of the semiconductor substrate 13.The microbridge structure 11 of FIG. 12 also provides for a larger fillfactor than a single level detector device disposed with the substrate13.

A thickness t of all of the layers 20, 21, 22, 23 and the distance dbetween the upper level 11 and the reflecting layer 18 may be chosen toachieve peak absorption over the desired operating wavelength band. Morespecifically, the thickness of layers 20-23 may be chosen to optimize athermal mass of the microbridge level 11 to achieve peak absorption overthe desired operating wavelength band, and the distance d may be chosento achieve constructive interference between any energy not initiallyabsorbed by the active area 32 that is reflected from layer 18, and theIR energy initially incident on the upper microbridge level 11.

FIG. 13 is a side elevation view of another embodiment of a detectordevice 100 according to the present invention. This embodiment of thedetector device 100 also has an elevated microbridge detector 11 and alower level 12. The lower level 12 may also include the ROIC 15 withinthe semiconductor substrate 13 as discussed above.

According to this embodiment of the detector 100 illustrated in FIG. 13,the detector device has a reflective concentrator 34 between themicrobridge level 11 and the lower level 12. The reflective concentratorconcentrates incoming IR radiation not initially detected by active area32 back onto the active area. Preferably, the reflective concentrator 34has a pixel collecting area having a dimension on a side l₁ in a rangeof 16-24 μm (for optical wavelengths in a range of 8 to 12 μm) and theactive area has a length on a side 1 ₂ of about 5 μm. The opticalconcentrator 34 acts to create the pixel collecting area of the detectordevice that is greater than the area of the active area.

FIG. 14 is a top plan view of the elevated microdetector level 11 of thedetector device of FIG. 13. This drawing is shown as though the activearea 32 is transparent to illustrate connections of the active area 32to metal leg interconnects 38 and 40. In a preferred embodiment, themetal leg interconnects connect to a top surface of the active area atrespective sides 39, 41 of the active area. However, it is to beappreciated that connections to any portion of the active area arepossible and are intended.

The concentrator 34 of this embodiment of the detector 100 is shaped toprovide the distance d between the upper microbridge 11 and a bottom ofthe concentrator 34, and so that the overall shape of the concentratorprovides constructive interference properties between energy notinitially absorbed by active area 32 and reflected by concentrator 34,and the energy initially incident on active area 32. Bridge layer 42 maybe chosen to reflect little radiation and generally to transmit asubstantial percentage of the incident IR radiation through to theconcentrator 34, which in turn concentrates the incident IR radiationback onto the active area 32 to provide the increased pixel collectionarea. The metal interconnects 38 and 40 are connected to the active area32 at the respective sides 39 and 41 of the active area 32 and provide adetected signal to the ROIC 15 at the lower level 12. The detectedsignal corresponds to the sensed change in resistance of the active area32. The metal interconnects 38 and 40 are constructed and arranged so asto continue down sloped walls 46 of the concentrator 34 to the lowerlevel 12 and make electrical contact with, for example, via holes 190that connect to contact pads 43 and 44 disposed on the lower level.

For each of the embodiments of the detector device described above,there is a need to reduce the size of the detector device and inparticular, the size of the active area 32 of the detector device, whilemaintaining an absorption sensitivity and while maintaining a thermaltime constant (t_(c)) to within a desired operating range. Inparticular, in a preferred embodiment of the uncooled IR sensor 104 ofthe present invention, the time constant is to be in a range of 5 to 20milliseconds for an IR wavelength band of operation in a range of 8-12μm. The lower limit of 5 milliseconds is a function of the frame rate ofthe IR sensor and the noise of the sensor, and the upper limit is afunction of a need to see fast moving scenery and a threshold abovewhich an eye will tend to see blurring of the displayed infrared signal.Referring to Equation (1), it is known to one of skill in the art thatthe time constant (t_(c)) of the detector device is equal to the thermalcapacitance (C) of the detector device divided by the thermalconductance (G) of the detector device.

$\begin{matrix}{t_{c} = \frac{C}{G}} & (1)\end{matrix}$

The thermal capacitance of the detector device is proportional to thesize of the active area of the detector device. In particular, thethermal conductance is, as will be discussed in greater detail below,inversely proportional to a length (l) of the conductive legs (see 38,40 in FIG. 4) coupling the active area 32 on the microbridge level 11 tothe substrate on the lower level 12. As the active area of the detectordevice is reduced, the thermal capacitance goes down and thus thethermal time constant t_(c) also goes down. In addition, when the sizeof the active area is reduced the absorption sensitivity of the detectordevice goes down. Thus, there is a tradeoff with each of the thermaltime constant and the sensitivity of the detector device, and the sizeof the detector device. The present invention seeks to reduce the pitchof the device including the size of the active area of the detectordevice while maintaining the thermal time constant to within the desiredoperating range and the sensitivity of a larger detector device.

One way to maintain the thermal time constant t_(c) to within thedesired operating range while decreasing the size of the active area isto increase the length (l) of the legs between the microbridge level 11and the semiconductor substrate 12, by an amount proportional to thedecrease in the size of the active area, to maintain the desired timeconstant. The length of the legs for this embodiment can be increased bywinding the legs around the reduced active area in the space given up bythe reduced active area. In addition, the sensitivity of the largerdetector device may be accomplished by the reflective concentrator 18,34 that enhances absorption of the incident energy with the smalleractive area thereby maintaining an optical sensitivity of larger activearea devices.

The thermal conductance (G) of the legs is determined as shown in thefollowing equation:

$\begin{matrix}{G = \frac{(K)(w)(t)}{l}} & (2)\end{matrix}$where G is the thermal conductance of the detector device; K is thethermal conductivity of the material used to provide the active area 32and the conductive legs 38, 40; between the microbridge level 11 and thesubstrate; w is a width of the legs; t is a thickness of the materialforming the legs and the active area, and l is the length of the legsbetween the active area 32 and the contact pads on the substrate 13. Inorder to fabricate detector devices of these dimensions, the width w andthe thickness t of the legs are typically fabricated to a certain sizelimited by the processing technology and also by the need to be able tosupport the upper microbridge level 11.

FIGS. 15( a), (b), (c) illustrate three different embodiments andmethods of fabricating the conductive legs 38, 40 of detector 10 (seeFIG. 12) and detector 100 (see FIGS. 13-14) according to the presentinvention. In FIG. 15( a), M1 is a mask used to form the leg metalconductor (LMET) between the upper microbridge level 11 and thesubstrate 12. In addition, M2 represents a mask that is used to form abridge or supporting layer on which the LMET will reside. As will bediscussed in greater detail below, typically the LMET may be made fromany of titanium-tungsten (TiW), vanadium oxide (V₂O₃), Nichrome (NiCr),or platinum. A problem with the structure and process for fabricatingthe conductive legs and bridge layer between the microbridge level andthe substrate as illustrated in FIG. 15( a), is that the process limitsthe leg width w of the conductive legs.

Referring now to FIG. 16, there are illustrated some of the processsteps for forming the conductive legs illustrated in FIG. 15( a). Inparticular, as will be discussed in greater detail below, one step ofthe process of forming the detector devices discussed above is toprovide a protective layer 16 above the semiconductor substrate 13.Deposited above the protective layer is a silicone nitride (SiNi) layer20 (step A). The leg metal layer 21 such as, for example, NiCr is thendeposited on the SiNi layer (step B). The leg metal layer is then maskedwith the mask M1 (see FIG. 15( a)) and etched to form the leg metalpattern 38 (step C). An additional SiNi passivation layer 23 may then bedeposited on top of the existing structure (step D). The structure isthen masked via mask pattern M2 and etched to form the leg and bridgestructure illustrated in FIG. 15( a) (step E).

It is to be appreciated that for this application, the minimum leg widthw is defined by the greater of the LMET width and the width of thebridge supporting the LMET (see FIG. 15( a). The above-described processresults in a minimum leg width of about 3.5 microns, wherein the LMETwidth is approximately 1.5 microns. The leg width w determines thethermal conductance of the connector device as discussed above withrespect to Equation (2). Accordingly, it is the goal of the presentinvention to be able to use the same processing equipment and to changethe leg width w and/or thickness to provide the detector device with abetter thermal conductivity G.

One embodiment of the present invention as is illustrated in FIG. 15( b)uses a method as will now be described to reduce the leg width w toyield a better thermal conductivity G which is used to offset a decreasein the size or pitch of the detector device. According to thisembodiment, the detector device of the present invention can be madesmaller (a smaller pitch), while maintaining the thermal time constantwithin the desired operating range discussed above and while maintaininga sensitivity of a larger detector device, using existing fabricationequipment technology.

FIG. 15( b) illustrates this embodiment of a leg structure according tothe present invention. It is to be appreciated that for thisspecification, this embodiment will be called the “co-aligned” legstructure. FIG. 17 illustrates the fabrication process for theco-aligned leg structure. Steps A and B for the co-aligned leg structureare the same as described above with respect to FIG. 16, except thatinstead of using NiCr as the leg 38 metal (LMET), TiW is preferably usedand deposited in step B. Mask M1 is used to pattern and etch the TiW toa width W1 that is wider than the final LMET width w, as illustrated inFIG. 15( b) (step C). As discussed above with respect to step D of FIG.16, a protective layer of SiNi is then deposited above the patterned TiWleg structure 38, as illustrated in FIG. 17 (step D). Mask M2 is thenused to pattern and etch both the SiNi layer 23 and the edges 28 of theTiW leg metal pattern to yield the structure illustrated in FIG. 15( b).One disadvantage of this structure is that the SiNi layer 23 does notcover the sides of the LMET. However this method and structure providean overall narrower leg width was compared to the structure of FIG. 15(a). In particular, for this embodiment, the leg width w may be reducedto approximately 1.5 microns.

Referring now to FIG. 15( c), there is illustrated another embodiment ofa leg structure according to the present invention. It is to beappreciated that this embodiment of the leg structure will be termed a“self-aligned” leg structure. The self-aligned leg structure hassubstantially the same leg width was the co-aligned leg structureillustrated in FIG. 15( b). However, the self-aligned leg structure hasa reduced thickness t as compared to the previously described legstructures. Referring to Equation 2 above, a reduced thickness t of theleg structure also yields a reduced thermal conductance G of thedetector device. FIG. 18 illustrates the process for fabricating theself-aligned leg structure. Steps A through D are the same as discussedabove with respect to the embodiment of FIG. 15( a) and illustrated inFIG. 16. The SiNi layer 23 is then masked and etched so that all nitride16, 23 is removed from the above and around the LMET, as illustrated instep E.

The detector devices 10, 100 of the present invention can be made withthe leg structures of FIGS. 15( a), (b), (c) as discussed above, toprovide a reduced sized detector device having an improved sensitivity.The leg structure illustrated in FIG. 15( a) when incorporated into thelegs 38, 40 of the detector 10 of FIG. 12 and having a pitch size of 48μm typically has a minimum temperature resolution on the order of 60°mK; whereas, the same detector device fabricated with the co-aligned legstructure illustrated in FIG. 15( b) may achieve minimum temperatureresolution on the order of approximately 30° mK; moreover, the samedetector device fabricated with and the self-aligned leg structureillustrated in FIG. 15( c) may achieve on the order of approximately 20°mK.

The detector structures 10, 100 of the present invention may befabricated using existing processing techniques. More specifically, foreither of the detector device embodiments, the ROIC 15 may be fabricatedat the surface 14 of the substrate 13 using a standard IC process. Thelayer of dielectric 16, such as for example silicon nitride, may then bedeposited on the IC 15 and the lower level 12.

The embodiment of the detector device 10 illustrated in FIG. 12 may befabricated with the steps now described. Following deposit of thedielectric layer 16, a thin film layer 18 of reflective material, suchas a metal film like Pt or Au, may be deposited. A layer of phos-glassor other easily soluble material 180 in the range of, for example, about1-2 microns thick may be deposited and sloped walls may be formed in theeasily soluble material. As discussed above, the layer of easily solublematerial may be chosen so that the distance d between the reflectivelayer 18 and the upper level 11 of the microbridge structure hasconstructive interference properties so that enhanced absorption isachieved over, for example, the 8-14 micron IR wavelength range. Thelayer of SiNi 20 may be deposited on top of this structure and on thesloped walls to form the sloped walls 20′. The resistive film layer 21that makes up the active area of the device may be deposited. It is tobe appreciated that the resistive film layer can be any of the materialsdiscussed above. The leg connections 38, 40 (not illustrated) down tothe substrate are then formed according to any of the leg embodimentsdescribed above; this step includes the step of providing the SiNipassivation layer 22, 22′ above the layers 21 and 20 and above the legs38, 40 on the sloped sidewalls 20′. A thin film metal absorbing coating23 may optionally be deposited on top of the upper microbridge level.Slots or windows (not illustrated) are then opened within the SiNi areasto provide access to the easily soluble phos-glass layer 180 beneath theSiNi layers 20, 22. The phos-glass is then dissolved from beneath theupper bridge level 11 to provide the detector structure having any oneof the above-described leg structures.

Referring to FIG. 19, the steps for fabricating the detector structure100 illustrated in FIGS. 13-14 will now be described. After thedielectric 16 has been deposited, the shape of the concentrator 34 isthen fabricated in either the dielectric layer 16 or in an additionaldielectric layer (not illustrated) deposited on top of the dielectriclayer 16. The sloped side walls 46 of the concentrator 34 can befabricated using standard sloped dry etch techniques of the dielectric.The shape and the depth d of the concentrator depend on the specifics ofthe cavity structure and detector device structure that is beingfabricated.

A surface 35 of the reflective concentrator 34 is then passivated with asecond dielectric layer 170, such as for example silicon nitride, thatwill not be etched by a subsequent etching step to remove a sacrificiallayer 180 such as, phos-glass, that is to be deposited on top of theconcentrator as will be discussed infra. At least one via contactopening 190 is then provided in the second dielectric layer 170 bymasking the second dielectric layer and etching via the contact openingthrough each of the second dielectric layer and the first dielectriclayer down to respective contact pads 43, 44 on the substrate level 12(See FIG. 14), or in other words down to the ROIC 15. A thin film layerof reflective material 200, such as, for example, metal film Pt or Au isthen deposited on the second dielectric layer to form the reflectivesurface of the concentrator 34 and to provide electrical connection fromthe electrical concentrator 34 to the contact pads 43, 44 of the IC 15.It is to be appreciated that the thin film layer of reflective materialis removed outside of the pixel area so that a plurality of detectordevices 100 can be provided that are electrically isolated from oneanother.

The sacrificial layer 180 of undoped glass, phos-glass, silicon dioxide,or other easily soluble material is then deposited on the reflectivesurface 200 of the concentrator to fill the reflective concentrator andto provide a substantially flat surface 192. It is to be appreciatedthat the concentrator filled with the soluble material can include athird layer of passivation (not illustrated) disposed above the thinfilm metal of the reflective concentrator, if so desired. As discussedabove, the depth d between the lower most point of the reflectiveconcentrator 34 and the microbridge level 11 is provided so thatincident electromagnetic radiation reflected by the concentrator 34 isreflected toward the microbridge level 11 and more specifically theactive area 32, and has constructive interference properties with theelectromagnetic radiation incident on the active area 32. An advantageof the concentrator 34 is that the sensitivity of the detector device100 is increased to provide a pixel collecting area that is larger thanthe area of the active area 32 of the detector device.

The various layers of the active area 32 are now deposited on thesubstantially flat microbridge surface 11. In particular, a firstsupporting layer 20, such as for example silicon nitride, is depositedon the substantially flat surface of the microbridge level 11. Aresistive film layer 21 having a high thermal coefficient of resistance(TCR), such as for example any of TiW, NiCr and VO_(x), is thendeposited on the first supporting layer to form the active area 32. Theresistive film layer is then masked and etched in a pattern to form atleast a part of the active area 32, and the leg structures 38, 40between the resistive layer 21 and reflective metal 200, describedabove, using any of the leg structures described and illustrated above.The resistive film outside of the active area 32 is also etched away. Athin film absorbing layer 23 such as, for example, silicon nitride or athin metal, may optionally be deposited on top of the resistive filmlayer if needed to increase absorption efficiency of the detector device100.

The thin film absorbing layer 23, the resistive film layer 21, and thefirst supporting layer 20 are then masked to define the shape of theactive area 32. The slots or windows may then be opened within the SiNiareas outside of the active area, and etched down to the sacrificiallayer 180 filling the reflective concentrator 34 to substantially exposethe sacrificial layer. The sacrificial layer is then dissolved using aselected etching process that removes the sacrificial layer withoutremoving the layer of the active area and the leg metal connections tothe reflective concentrator 34 so that the active area 32 is suspendedover the concentrator 34, is thermally isolated from the lower substratelevel 12 and electrically connected to the substrate level 12 by themetal interconnects 38, 40 and the vias 190.

An advantage of the embodiment 100 of the detector of FIGS. 13-14 isthat the concentrator 34 can be provided between the active area 32 andthe substrate level 12 using conventional processing techniques. Inaddition, it is to be appreciated that another advantage of the detectorembodiment 100 is that the metal interconnects 38, 40 connecting theresistive film layer 21 of the active area 32 and the integrated circuit15 on the substrate level 12 are formed through the reflectiveconcentrator 34, eliminating any need to use space outside of thereflective concentrator to provide the metal interconnects.

FIG. 20 illustrates a photo of the detector device 10 according to thepresent invention. In FIG. 20, there is illustrated a mesa point (MP)which connects the legs 38, 40 down to the ROIC 15 in the semiconductorsubstrate 13. The MP contact 190 ultimately contributes to an overallsize or pitch of the detector device and thus to the pixel size withinthe FPA 102 of such detector devices. It can be seen that the MP contactis shaped like a basket, wherein a top of the basket is within the areadedicated to providing the detector device and a bottom of the basket iscoupled to the substrate 13 (see FIGS. 13-14). A problem with this MPcontact structure, as is illustrated in FIG. 20, is a percentage of thearea that may be used to form the detector device is occupied or lost bythe top of MP contact. Accordingly, one embodiment of the detectordevice 10 of the present invention is modified so that the MP contactvia is inverted and so that the smaller dimension of the MP contact iswithin the area used to provide the detector device and the largeropening of the MP contact is coupled to the semiconductor substrate.

FIG. 21 illustrates a cross-sectional view of the inverted MP contactvia 188. The inverted MP contact via, as discussed above, provides aconnection between the conductive legs 38, 40 coupled to the resistivelayer 22, and the contact pads 43, 44 on the semiconductor substrate 13.An advantage of this inverted MP contact is that more area is availableto provide the detector device. Therefore, the pitch of the detectordevice 10 using the MP contact can be reduced, for example, from a 46micron pitch to, for example, approximately a 28 micron pitch. Thisallows the detector device 10 of the present invention to be used notonly with a video standard, necessitating an FPA 102 havingapproximately 328×240 pixels which was achievable with the detectordevice having a 46 μm pitch, but also to be used with, for example, ahigh definition TV (HDTV) standard which typically requires the FPA ofdetectors having on the order of 640×480 detectors. Thus, an advantageof this embodiment of the detector having an inverted MP contact is thatthe number of detectors can be increased by approximately four times andthe FPA can have approximately four times the number of pixels.

The embodiment of the detector 10 having the inverted MP contact via 188illustrated in FIG. 21 is fabricated with the steps now described withreference to FIG. 22. During fabrication of the ROIC 15 (see FIG. 12), ametal contact pad 43 is deposited on the semiconductor substrate 13. Themetal can be, for example, platinum or NiCr. The metal may be planarizedand a protective layer of dielectric 16, such as SiNi may be depositedon the metal contact pad and the ROIC (step A). The protectivedielectric layer is then patterned with a mask and photo resist 17 and ahole 24 etched through the dielectric layer down to the metal contactpad for a connection to the metal contact pad (step B). A layer of metal19 is then deposited over the protective dielectric layer and throughthe hole 24 down to the contact pad. The layer of metal may be forexample, platinum or Nichrome (step C). A layer of dielectric 25 maythen be deposited to fill the hole 24 making the connection down to thecontact pad and the layer of dielectric may be planarized to beconsistent with the top of the metal layer 19 (step D). It is to beappreciated that the dielectric can be, for example, either an oxide ora nitride and that no dielectric may be necessary if the dimensions ofthe contact hole are small compared to the operating wave length of thedetector. Another layer of dielectric 27 such as, for example, oxide ornitride may then be deposited having a thickness that is to be athickness of the inverted MP contact (step E).

The layer of dielectric 27 may then be patterned and covered with aphoto resist layer 29 and etched to form a mesa dielectric 30 (step F).It is to be appreciated that although not illustrated in FIG. 22, themesa dielectric 30 can also be located over the via hole 24 down to themetal contact pad 43 if the base of the MP contact, (the largerdimension of the MP contact) is larger than the diameter of the via holedown to the metal contact 43. A layer of metal 31 may then be depositedover the substrate to fill in the via hole 24 and to form the MP contact188 (step G). Both metal layers 19, 31 may then be patterned with aphoto resist by a mask and etched to define the contact from the contactpad 43 to the top of the MP contact 188 (step H). It is to beappreciated that at this point the reflector 18 (not illustrated) suchas described above with respect to FIG. 12 may also patterned andetched.

As discussed above with respect to FIG. 12, a layer of phos-glass 180 orother easily soluble material having a thickness in the range of, forexample, 1-2 microns is then deposited on the substrate 13 (step I). Thethickness of the layer 180 may be chosen to be in a range ofapproximately one quarter of a wavelength of the operating wavelengthband and sloped walls may be formed in the easily soluble material, asdiscussed above. A layer of nitride 20 such as, for example, SiNi maythen be deposited on top of this structure and on the slope walls toform the sloped walls 20′ (step I). As discussed above, the resistivefilm layer 21 such as, for example, VO_(x) that makes up the active area32 of the device 10 may then be deposited on top of the nitride layer(step J). It is to be appreciated that as discussed above, the resistivefilm layer can be any of the materials discussed above such as, forexample, the co-aligned leg structure and the self-aligned legstructure.

The various leg connections discussed above from the active area 32 downto the top of the inverted MP contact 188, may then be formed. Inparticular, the layer of nitride 20 is masked, resist 33 is depositedand the nitride 20 is etched to form hole 36 above the inverted MPcontact 188 (step K). Another layer of nitride 8 (not illustrated) suchas, for example, SiNi may then be deposited, patterned with a photoresist layer 37 and etched to form holes 45, 47 in the SiNi layer abovethe inverted MP contact and above the resistive film layer (step L). Ametal layer (LMET) such as, for example, Nichrome or TiW may then bedeposited over the nitride layer 8 and through the holes 45, 47 tocontact the resistive film layer 21 and the top of MP contact 188through the holes in the nitride layer (step M). The leg metal layer 9is then patterned and etched according to any of the above describedprocesses for providing any of the above-described leg metal structuressuch as, for example, the self-aligned leg metal structure to form thelegs 38, 40 having the dimensions described above (step N).

An additional layer of nitride 22 such as, for example, SiNi may then bedeposited over the structure (step O). It is to be appreciated thatalthough not illustrated in the FIG. 22, an additional thin film metalabsorbing layer 23 (see FIG. 12) may be optionally deposited on top ofthe active area 32 on the upper microbridge level. Slots or windows arethen opened within the SiNi layer 20, 8, and 22 to provide access to theeasily soluble phos-glass layer 180 beneath the SiNi layers 20, 8 and 22(step P). The phos-glass 180 is then removed from beneath the upperbridge level 11 to provide the detector structure 10 having any one ofthe above-described leg metal structures 38, 40 and the inverted MPcontact down to the contact pad 43.

According to another embodiment of the uncooled infrared sensor 104 (seeFIG. 1) of the present invention, any of the above-described detectordevices 10 can be placed in the FPA 102 and configured as shown in FIG.23 to share a single contact such as, preferably, the inverted MPcontact 188 between two of the detector devices. This provides anadditional space saving within the FPA. It is to be understood that thisembodiment of the FPA sharing a single contact between two detectordevices will be termed a “single-contact per pixel” design. In order toprovide a single contact per pixel FPA, circuitry may be provided withinthe ROIC 15 (see FIG. 1) that switches between each of the detectorsassociated with each shared contact. Access to any of the columncircuitry 92 discussed above (see FIG. 2) through any shared contact maygo through for example, a multiplexer (not illustrated) disposed withinthe ROIC that performs this switching function. An advantage of thisembodiment of the FPA is that it minimizes the is effect of eithercontact 188, 190 defects or the conductor leg defects; without suchcircuitry, for example, an entire column may not be usable when there isa single defect within a column of the FPA. In contrast, the singlecontact per pixel design FPA reduces the amount of space required in theFPA and allows any contact defect to be limited to a particular pair ofdetectors that share the contact.

FIG. 24 illustrates another embodiment of a FPA 102 using anotherembodiment of a leg design 38′, 40′ that can be used with any of theabove-described detector devices 10. It is to be understood that thisembodiment will be referred to as the “folded leg” design. In thisembodiment, the legs 38′, 40′ from the upper bridge level 11 (see FIG.12) down to, for example, the MP contact 188 discussed above are foldedto maintain a desired leg length l, so as to provide the thermalisolation, the desired time constant t_(c) and to provide a better fillfactor. In particular, the folded legs 38′, 40′ permit an aspect ratioL/W of the active area 32 to be greater. It is to be understood that theaspect ratio of the active area is the length L divided by the width Wof the active area. The folded legs 38′, 40′ of this embodiment allowthe active area to be shaped such as, for example, as illustrated inFIG. 24 in the form of rectangle, which has about a 2-to-1 aspect ratio.In contrast, the above-described embodiments of detectors 10, 100 havebeen illustrated with approximately 1-to-1 aspect ratio for the activearea 32, or, in other words, approximately a square shaped active area.The increased aspect ratio allows the resistance of the detector deviceto be increased by a factor of two. An advantage of increasing theresistance of the detector is that the sensitivity of the detectordevice is increased proportionally to the increased resistance.Therefore, for example, by increasing the aspect ratio by two, thesensitivity of this embodiment detector device 10 of the uncooled IRsensor can be doubled.

In still another embodiment of any of the detector devices 10, 100described above, an overall operating band width or wavelength band ofoperation of the detector device can be increased, for example, byadding an additional layer of, for example, VO_(x) to the active area 32of the detector device. FIG. 25 illustrates a graph of an Absorptance(%)versus wavelength (in μm) of the above-described detector device 10 (seeFIG. 12) without the added layer of VO_(x) 72 and with the added layerVO_(x) 73. It can be seen from FIG. 25 that with the additional layer ofVO_(x), the wavelength band of operation is increased from, for example,approximately 8 to 14 microns as illustrated for curve 72, toapproximately 4-14 microns as illustrated for curve 73. This increasedwavelength band of operation may allow any of the uncooled IR sensordevices to be used, for example, over two wavelength bands of operation.In particular, the uncooled IR sensor may be used, for example, inthreat warning applications to provide a higher probability of detectionand reduced false alarm rates by using the uncooled IR sensor over twoseparate and distinct wavelength ranges of operation such as, forexample, 10 to 14 μm and 4 to 8 μm. Such operation of the device 104helps to eliminate a problem called contrast inversion which typicallyresults when various targets that have different temperatures andemissivities have the same radiant emittence in a spectral band ofoperation. Therefore, an advantage of this embodiment of the uncooled IRsensor including the wider band detector device is that it can be usedover such separate wavelength bands of operation to improve performanceby reducing false alarms and providing a higher probability ofdetection.

Any of the above described detector devices can be placed in an arraythereby forming the FPA 102 (see, for example, FIG. 10). It is to beunderstood that any of the microbridge detector devices discussed abovecan be used in the FPA of FIG. 10. In one embodiment of the presentinvention, an array of such detectors includes 480 detector devicesdisposed in rows along the y direction by 640 detectors disposed in acolumns along the x direction, wherein each detector or pixel devicecovers an area or pitch of about 28 microns on a side. The semiconductorarray operates over the IR wavelength range of 8-14 μm, and has an IRsensitivity of at least 80%.

As discussed above with respect to FIG. 1, the FPA 102 can be used in anuncooled infrared sensor 104 such as is illustrated in FIG. 1. Theuncooled IR sensor provides a two-dimensional, real-time display of animage for an operator of the uncooled IR sensor to view. For example, inan preferred embodiment of the uncooled IR sensor of the presentinvention, the uncooled IR sensor is configured to operate over at leastone IR wavelength band of interest. With the uncooled IR sensor of thepresent invention, the operator can view thermal signatures of objectsand/or scenery under conditions where the human eye would notnecessarily be able to see the objects and/or scenery. For example, theuncooled IR sensor may be used at night, in the day without washoutconditions, in the presence of smoke, in degraded weather conditions andthe like. One embodiment of an uncooled IR sensor of the presentinvention is a head mounted imaging system 120 as illustrated in FIGS.26 a, 26 b and 26 c. FIG. 26 a illustrates a helmet mountedconfiguration of the head mounted uncooled IR sensor, and FIG. 26 billustrates a goggle configuration of the head mounted uncooled IRsensor, and 26 c is an enlarged view of the uncooled IR sensor byitself.

FIG. 27 illustrates a block diagram of the head mounted uncooled IRsensor 120 of FIGS. 26 a, 26 b and 26 c. It is to be appreciated thatparts similar to the uncooled IR sensor illustrated in FIG. 1 have beenidentified with similar reference numbers and any description of theseparts is not repeated here. With the head mounted imaging system of FIG.27, an electromagnetic signal may be focused by the optics 106 onto thefocal plane array 102. The focal plane array 102 may be temperaturestabilized as discussed above, with the aid of temperature stabilizingcircuitry 124 contained within the FPA assembly. The focal plane array102 may convert the focussed signals into sensed signals and may outputthe plurality of the sensed signals to the focal plane array processor108. The focal plane array processor may amplify and digitize each ofthe plurality of sensed signals with a preamplifier andanalog-to-digital converter 126, and may output the plurality ofprocessed signals to the display processor 110. The focal plane arrayprocessor may also include a programmable logic device (PLD)128 thatprocesses the plurality of processed signals to correct any offsets orgain differences between the plurality of processed signals, toeliminate any bad signal data and to equalize the data, as discussedabove. It is to be appreciated that these functions may be done with anycombination of hardware and software, as discussed above, and suchmodification is intended. The display processor may reformat thecorrected signals and convert the corrected signals to an analog signalvia the digital-to-analog converter 130, so that the analog signal is ina format suitable for display. The display processor 110 may alsoinclude a symbology generator 125 for providing symbols on the display.The display driver 132 may then output the analog signal to the display112 for display to the user.

As discussed above, the controller 114 may provide automatic and/ormanual control of the display processor 110 to provide automatic and/ormanual adjustment of the uncooled IR sensor 104 and of various displayparameters. The controller of the head mounted system 120 may includeswitches 115 in a control panel, and a microprocessor 117. In addition,the supply electronics 116 may include batteries 119, or a connector forexternal power 121, as well as power conditioning circuitry 123.

In a preferred embodiment of the head mounted system 120, the focalplane array 102 may be operated in at least one IR wavelength band, forexample over the 8-14 μm range. In addition, the display 112 may beeither a one-eye or two-eye display for the system user, and may beadjusted with the aid of the controller 114. In the preferredembodiment, the focal plane array processor 108 and the display 112 maybe mounted in the helmet or within the face-mounted goggles. Inaddition, the display processor 110, the controller 114, and the supply116 may be provided in a unit that can be vest mounted. However, it isto be appreciated that any variation known to one of skill in the art,such as for example, mounting each of the above in the helmet orgoggles, is contemplated and intended to be within the scope of thepresent invention.

An advantage of the head-mounted imaging system 120 of the presentinvention is that it is a self-contained, portable unit having a reducedsize, weight and power consumption. In particular, the focal plane array102 does not require cooling, or mechanical scanners or choppers asrequired by prior art devices. In addition, the preferred embodiment ofthe head-mounted system may not include a shutter (see FIG. 1) andinstead, may use the manual or automatic optics and defocused scene tocalibrate the sensor, as discussed above. The head mounted system mayoperate in darkness, in the daytime without washout conditions incontrast to prior art devices that use an image intensifier tube, canpenetrate smoke, and the like. Thus, for the reasons discussed abovewith respect to the detector device and the focal plane array, the headmounted system has an improved reliability and sensitivity as comparedto prior art devices.

Another embodiment of an uncooled IR sensor of the present invention isa hand-held imaging system such as is illustrated in FIGS. 28 a, 28 band 28 c. The hand-held imaging system may be a monocular system 134such as illustrated in FIG. 28 a or a binocular system 136 such asillustrated in FIGS. 28 b and 28 c. It is to be appreciated that partssimilar to the uncooled sensor of FIG. 1 are labeled with similarreference numbers, and any description of these elements is notrepeated. The monocular system of FIG. 28 a may include a window 127having an optical filter 122 disposed in front of the IR optics 106, anda focus ring 129 that focuses the incident electromagnetic radiationonto the IR optics. In addition, the display 112 may include an eyepiece 131 which acts in combination with a CRT or FPD 133 to provide thedisplay. The eye piece display 112 may also have a diopter adjustment135, and a focus knob 137, as known to one of skill in the art. In apreferred embodiment of the hand-held imaging system of FIGS. 28 a, 28 band 28 c, the supply electronics 116 may be a battery, and the focalplane array may operate over at least one IR wavelength range to yield along range IR telescope or binoculars that can be used in darkness, indaylight, to penetrate smoke, and the like. The long range telescope andbinoculars are self-contained units having a reduced side, weight andpower consumption, while providing an increased reliability andsensitivity.

A further embodiment of an uncooled IR sensor of the present inventionis a weapon sight 140, such as is illustrated in FIGS. 29 a-29 b. FIG.29 a illustrates a top view of the weapon sight according to the presentinvention, and FIG. 29 b illustrates a block diagram of the weaponsight. It is to be appreciated that parts similar to the uncooled IRsensor of FIG. 1 are identified with similar reference numbers, and anydescription thereof is not repeated. The weapon sight may also include acover 139 that covers the lens 106, a focus ring 129 for adjusting thefocus of the focused signals from the lens 106 onto the focal planearray 102, a compass 141, and a global positioning system (GPS) antenna143. The display processor 110 may include additional electronics forprocessing the GPS signal and the compass information. In a preferredembodiment of the weapon sight of FIGS. 29 a-29 b, the optical lens 106may also include a filter, the supply electronics 116 may be batteries,and the display 112 may include the eye piece, a CRT or FPD 133, and afocus adjustment knob 135. The preferred embodiment may be operated inat least one desired IR wavelength band of interest to provide along-range weapon sight, such as a rifle mount, that can be used topenetrate darkness, to penetrate smoke, can be used in the daytime, andthe like. The weapon sight 140 may be a self-contained unit having areduced size, weight, and power consumption, while providing anincreased reliability and sensitivity.

Still another embodiment of an uncooled IR sensor of the presentinvention is a miniature camera/recorder (hereinafter a “camcorder”)such as is illustrated in FIGS. 30 a-30 b. FIG. 30 a illustrates across-sectional view of the camcorder, and FIG. 30 b is a block diagramof the camcorder. It is to be appreciated that parts similar to theuncooled IR sensor of FIG. 1 are identified with similar referencenumbers, and any description thereof is not repeated. The camcorder mayinclude a recorder 152 for recording signals on a suitable recordingmedium 154. It is to be appreciated that the recording medium can be anyrecording medium known to one of ordinary skill in the art such as, forexample, a magnetic recording tape of a VHS, 8 mm, or BETA format. In apreferred embodiment of the camcorder, the display 112 may include aview finder 145 as well as a CRT or FPD 133. In addition, in thepreferred embodiment the supply electronics 116 may be a rechargeablebattery pack, and the controller 114 may include control knobs 147 andelectronics for rewinding, fast forwarding, and playing back therecording medium. The camcorder may be used in at least one IRwavelength band of interest to provide a long-range camcorder that canbe used at night, in the daytime, to penetrate smoke or inclementweather, and the like. In addition, the camcorder may be aself-contained unit having a reduced size, weight and power consumptionand also having an increased reliability and sensitivity.

Yet another embodiment of an uncooled IR sensor of the present inventionis a microscope 160 such as is illustrated in FIGS. 31 a-31 b. FIG. 31 aillustrates a side elevational view of the microscope and FIG. 31 billustrates an operational block diagram of the microscope. It is to beappreciated that parts similar to the uncooled IR sensor of FIG. 1 areidentified with similar reference numbers and that any descriptionthereof is not repeated. The microscope may include a microscope base153 having a position adjuster 155, and a specimen or integrated circuitmask 151 which is backlit by a light source 149, as is known to those ofskill in the art. In a preferred embodiment of the microscope, thedisplay 112 may include a CRT or FPD 133, the controller 114 may includemanual control knobs 147 and the optics 106 may include a front surfacemirror 157. The microscope can be used over at least one IR wavelengthband of interest, for example, from 8-12 μm, with the aid of filter 159to provide multi-spectral images with the microscope.

Still, another embodiment of an uncooled IR Sensor of the presentinvention is the imaging radiometer/spectrometer such as is illustratedin FIGS. 32 a-32 b. FIG. 32 a illustrates a cross-sectional view of theimaging radiometer/spectrometer 171, and FIG. 32 b illustrates a blockdiagram of the imaging radiometer/spectrometer. It is to be appreciatedthat parts similar to the uncooled IR sensor of FIG. 1 are identifiedwith similar reference numbers and any description thereof is notrepeated. In the imaging radiometer/spectrometer, the lens 106 can beeither one of a spectral-splitting lens 172, which may be used toprovide a spectrometer, and an imaging lens 174 that may be used toprovide the radiometer. The imaging radiometer may be used to measure atemperature of a scene on which the radiometer is focused, and thespectrometer may be used to measure an energy or power emitted by thescene as a function of the wavelength at which the scene is emitting theelectromagnetic signal.

The radiometer/spectrometer may also include a lens mount 161 formounting either of the spectral-splitting lens 172 and the imaging lens174, and a tripod mount 163 for mounting the radiometer/spectrometer toa tripod. In the preferred embodiment of the radiometer/spectrometer,the display 112 may include a CRT or FPD, the controller 114 may includemanual control knobs 147, and the supply electronics may includerechargeable batteries 164 as well as a 110 volt AC connector 165. Theradiometer/spectrometer can be used in at least one IR wavelength bandof interest at night, in the daytime without washout conditions, topenetrate smoke, and to penetrate inclement weather. Theradiometer/spectrometer is a self-contained unit having a reduced size,weight and power consumption while also having an increased reliabilityand sensitivity.

As discussed above, any of the uncooled IR sensors have the capabilityof seeing through smoke which is often impervious to the human eye.Accordingly, one application of any of the above-described uncooled IRsensors is for use in fire fighting. The uncooled IR sensor 104 (seeFIG. 1) of the present invention offers the fire fighter the ability toenter a smoke filled building and see through the smoke, throughdoorways, the fire location, and the like to locate fire victims undercircumstances where the fire fighter might normally not have anyvisibility. For example, the fire fighter may use the head mountedembodiment of the uncooled IR sensor of the present invention asdiscussed above and illustrated in FIGS. 26 a, 26 b and 26 c.

One problem that may result from using any of the above-describeduncooled IR sensors for the fire fighting application is that theequipment may be exposed to intense heat such as is encountered in firefighting and other hot environments, and the resulting change in theoperating ambient temperature may obscure the actual signal informationof interest. Overheating of the sensor may also reduce the operatinglifetime of the uncooled IR sensor. Accordingly, the housing of any ofthe above-described uncooled IR sensors when to be used in hotenvironments, may be made of fire resistant materials and/or coldshielded, as discussed above, so that the sensor can continue to operatein such high temperature environments. One example of a fire resistanthousing may include a housing having double walls with the regionbetween the double walls of the housing containing an insulatedmaterial. The insulating material may slow the transfer of heat from anouter wall of the double walls to an inner wall of the double walls ofthe housing. Another embodiment of a housing may include a heat sink 175such as illustrated in FIG. 3 and known to those of skill in the art,disposed within the FPA assembly 90 that helps to prevent theelectronics from over-heating. Still another embodiment may include amaterial which undergoes a phase change from, for example, a solid to aliquid or a liquid to a gas to a function of temperature. A housing madeof such phase change material may reach a certain temperature threshold,and the housing may begin to go through the phase change and absorb heatfrom, for example, the electronics and to thereby retarding additionaltemperature rising of the electronics, and thereby extending theoperating life of the uncooled IR sensor. The phase change material mayalso be provided within any of the above-described uncooled IR sensorsas an insert module that is thermally connected to the electronics to beprotected and that is either removable or permanently affixed to suchelectronics. For example, the phase change material may be attached ormade part of the removable battery so that it can be replaced with afresh battery and a new phase change insert when, for example, thebattery is to be replaced.

One advantage of using any of the above-described uncooled IR sensorsfor the fire fighting application is that the sensor can be used todetect hot regions and may present a colorized display, as opposed to ablack and white display, image of any hot regions observed with thesensor to the operator. For example, a specified color can be isprovided for any region above a specified temperature. This feature maybe used, for example, to indicate that a certain object is about tocombust. In addition, another advantage of using the above describeduncooled IR sensors for the fire fighting application is that thedetector devices described above are DC coupled and therefore can bemapped to a display for example with the equalization controller 58 (seeFIG. 4), as discussed above, to provide both a positive and a negativetemperature dynamic range that may be viewed with the sensor. Inparticular, because the sensor is DC coupled, the above-describedsensors allows a viewer to simultaneously view hot objects and coldobjects within a same scene, as may be necessary, for example, for afire fighter to move within a smoked filled room without running intohot objects such as for, for example, a fire, or a wall or a ceilingbehind which there is a fire, or to find cold or warm objects such as,for example, an unconscious fire victim. Further another advantage ofthe uncooled sensor is that the uncooled IR sensors may automaticallyadjust, as described above, the operating point or temperature of thesensor to compensate for increases in background or scene temperaturethereby enabling further increases in the operating temperature dynamicrange of the uncooled IR sensor. Furthermore, the automatic or amechanical iris such as, for example, the electronic shutter or themanually focusable optics may further help to reduce the amount ofoptical energy incident on the FPA and to thereby enable a broaderdynamic range of signals to be processed with the uncooled IR sensorswithout saturating the uncooled IR sensor. Moreover, the uncooled IRsensors have the ability to adjust the integration time of the FPAassembly as described above to, for example, less than 16.6 millisecondsor in other words so the system may operate at a 60 Hz frame rate. Theshort integration time may be a way to reduce the amount of incidentenergy on the FPA and to extend the operating dynamic range of theuncooled IR sensors for such an environment. Still another advantage ofusing the above described uncooled IR sensors for this application maybe that the sensor allows hands-off operation and adjustment, eitherautomatically or manually, of the displayed signal to present an optimumimage to the fire fighter.

Another application for which any of the above-described uncooled IRsensors may be used is for border surveillance of, for example, theU.S.-Mexico border. In particular, FIG. 33 illustrates a bordersurveillance system 177 according to an embodiment of the presentinvention. The border surveillance system may have a plurality ofuncooled IR sensors 199, mounted on poles (P₁, P₂, P₃ . . . ) andinterfaced to, for example, a command post 178 to monitor the border 179for any human, or vehicular passage across the border. It is to beunderstood that although in FIG. 33 three sensors are illustrated, it iscontemplated that many more sensors may be disposed along the border.Each sensor may be provided on a pole to provide the sensor at a certainaltitude and to obtain a certain field of view (FOV₁, FOV₂, FOV₃ . . . )with each sensor. As illustrated in this FIG. 33, the sensors may bedisposed so that their fields of view overlap and so as to supplyredundant information with each sensor. It is to be appreciated thatalthough the border as shown in FIG. 33 is illustrated as theU.S.-Mexico border, the border surveillance system may be used at anyborder and the sensors need not be disposed directly at the border butcan be disposed anywhere such an application of this system is desired.

Each sensor may be coupled via cabling 181 to command post 178. Thecommand post may have a plurality of displays 183, 185 and 187 that maydisplay any of humans, vehicles and the like and the location at whichthey may be crossing the border. Any of the sensor signals can bereviewed on the displays, for example, by National Guard or BorderPatrol personnel.

One advantage to using any of the above-described uncooled IR sensorsfor this application is that the sensors can be calibrated to detectwhen a person at a temperature of, for example, approximately 98° iswithin the field of view of the sensor. In particular, referring to FIG.34, each sensor may be provided with a processor 186 that searches for ahuman target at such a temperature. If a person crosses within the FOVof any of the plurality of sensors, an alarm signal 178 may be providedby the sensor to the command center 178. In particular, each sensor mayhave a memory including a matched filter 189 of a typical thermalsignature of a human being. The matched filter 189 patterns arecorrelated to the image resulting within the sensor display pixels, andis used to identify the portions of the array display that highlycorrelate to a human target. A similar matched filter can be disposedwithin the sensor for other expected images such as, for example,vehicles 191 and animals 193. This matched filter information is usefulfor is statistical optimization of the sensors and so as to prevent anyfalse alarms. The sensor may also include a video processor 195 thatinclude components of either or both of the FPA processor 108 and thedisplay processor 110, discussed above. The sensors, after identifying atarget, send the alarm signal on line 187 and video information on line194 to the command center which displays the target on the display 183,185 and 187, thereby identifying the object and the particular locationalong the border where the target has crossed the border. Theinformation can then be used in whatever manner desired by the BorderPatrol such as, for example, to dispatch a team to the location toprevent illegal immigrants from crossing the border. It is to beappreciated that the command center can be located at a command postalong the border, at a remote location, or even tied to the Internet forremote monitoring and so that the information can be monitored by any ofa plurality of end users.

FIG. 35 illustrates one embodiment of an uncooled IR sensor 199 disposedon a pole P1 as discuss above. The sensor may include automaticallycontrolled zoomable optics 106 that may be controlled remotely, forexample, by a computer or automatically via the automatic zoom asdiscussed above. In addition, the sensor preferably includes an allweather encasement 196.

In one embodiment of the uncooled IR sensor 199 of the bordersurveillance system 177 of this invention, the sensor is calibrated andfocused so that a person may take up one pixel of resolution. It is tobe appreciated that a person can be imaged or detected with less thanone pixel of resolution or with a plurality of pixels of resolution andthat such modifications are intended. Accordingly, in this embodimentwhere the FPA 102 has an array of 328×246 pixels or detectors, the areathat can be viewed with the sensor may cover about 327 people in thehorizontal dimension along the border for a single uncooled IR sensor.If a typical person is approximately 1½ feet wide, then the widthdimension that each sensor may cover is about 500 feet along the border.Accordingly, at least 10 sensors may be needed for every mile along theborder. However, since the average person is approximately 6 feet highand since the FPA may also be 246 pixels in height, in reality only theheight dimension need be monitored. Therefore, by using the heightdimension for sensing an image, the number of sensors required along theborder may be reduced by a factor of approximately four. Moreover, thisfactor can be reduced even more such as, for example, by a factor of twoif any redundancy is removed so that the sensors no longer overlap theirfields of view. Accordingly, a minimum number of sensors along a 1,000mile border may be on the order of approximately 1,250 sensors. It is tobe appreciated that any number of sensors may be used including agreater number or a lesser number depending upon the resolution andcoverage desired and such modifications are intended.

In the preferred embodiment of the border surveillance system of theinvention, each sensor should be spaced apart at such a distance thatthe overall system is able to detect that there is a person or a vehiclecrossing the border at a given location and prevent a false alarm dueto, for example, an animal crossing the border. The range for which asensor is to be used determines its resolution. Accordingly, the numberof cameras may be chosen to ensure that the resolution equals or exceedsthe desired resolution at the border. Alternatively, the preferredembodiment may also introduce distortion into the optics so that the FOVis the same remotely from the camera as it is at the camera. Stillanother manner for varying the resolution achievable with each sensor199 is to vary the pixel sizes along the width of the FPA, wherein theyare greater in the middle of the array and smaller at the edges of thearray. In order to satisfy the Nyquist criteria, it is preferred that atleast 0.75 cycles per object are covered, so that 1.5 pixels arededicated to each object. However, more cycles and thus less pixels canbe used for an object standing still.

Still another application for any of the above-identified uncooled IRsensors may be to view the “limb”, or in other words, the earth'satmosphere, from an orbiting satellite looking tangentially to theearth's surface, or above the earth's surface as illustrated in FIG. 36.A limb sounder, as is known to those of skill in the art is used todetect gas constituents such as, for example, CO, at known distancesfrom the sensor thereby creating a picture of the gas contents at aparticular depth from the sensor. In particular, the limb sounder lookswith tangential scans 220, 222, 224, 226 as the satellite on which thelimb sounder is mounted orbits the earth. FIG. 36 illustrates limbsounding with the satellite at three different orbital positions 221,223, 225. The sensor can be operated in a manner such that a one timeinstance a frame is captured by the sensor for a measurement at aparticular depth from the sensor. As the satellite moves around theearth in orbit and a right fraction of a second later, another frame isthen captured. The next row or column of the FPA then views the samelimb sample as was previously viewed in the prior frame, and the samplescan be added and averaged to provide an averaged signal. The limbsounder may be used, for example, by a weather satellite to determinehow much ozone is at the earth's surface, or how much CO₂ is createdfrom, for example, by burning the rain forest in South America, and thelike. An advantage to using any of the above-identified uncooled IRsensors in this application is that the sensing is done in the IRwavelength range. In addition, because the sensor need not be cooled,less space and power constraints are required with the uncooled IRsensors of the present invention. In addition, the atmosphere alsoprovides natural cooling of the sensors thereby improving theirperformance.

FIG. 37 illustrates a block diagram of a uncooled IR sensor 230 that maybe used for limb sounding. It is to be appreciated that parts similar tothe uncooled IR sensor 104 of FIG. 1 are given like reference numeralsand that any discussion with respect to these parts is eliminated. Thesensor may include, a steering mirror 231 that is moved by motor 232 tofocus the FOV of the sensor that is presented to optics 106 and the FPA103. The steering mirror may provide various views such as a limb viewwherein the device is being used as a sounder, and a space view whereinthe device is looking at space to be used as a cold body forcalibration. In addition, the sensor may include a black body calibrator235 that presents a uniform scene to the sensor optics and FPA so thesensor can be calibrated, as discussed above. The sensor can also beplaced in the black body viewing position in certain orbit positions toprotect the optical filters and detectors when the sun would be withinthe limb view. Thus the steering mirror 231 provides several functionsincluding: periodic on board calibration of a black body, space viewing,viewing over the poles off the velocity vector and fast responserejection of a direct view of the sun. The sensor may also include aband pass filter assembly 236 which is preferably a filter wheel thatspins at a constant velocity under control of motor 237 so as to providemeasurement of a plurality of narrow vertical resolution cells ng a samefield of view.

The band-pass filter wheel may provide four optical channels, two CO₂temperature channels, one ozone channel and one window channel. It mayconsist of four multi-layer interference filters on a germaniumsubstrate mounted in the filter wheel. The sensor may view the limbthrough the filters, with an immediately time-adjacent view of the blackbody calibrator through the same filter, so as to track the drift of thesensor.

The sensor may also include the control electronics 114 and the signalprocessing electronics 102, 110 as discussed above with respect toFIG. 1. The signal processing electronics perform offset, gain, andcorrection as discussed above. The control electronics samplehousekeeping data and provide closed-loop control of the steeringmirror, an aperture cover door 238, the filter wheel 236 and motors 232,237. The thermal electric cooler 34 provides temperature control to theFPA and to the band-pass filter assembly for accurate calibration andfor accurate measurements.

In one embodiment of the limb sounder 230 of the present invention, afully baffled 3-element optical system provides viewing of the limb from10 km below the earth's surface to a 60 km altitude above the earth'ssurface. This view is taken with the FPA having 245 columns of detectorsand 327 rows of detectors to yield a total focal plane array size of11.33 mm by 15.1 mm. An image size can be narrowed on the FPA to provide188 pixels of resolution in azimuth by 3 pixels of resolution inelevation, or in other words a total picture image size of 8.7 mm by2.43 mm. The filter wheel may be rotated at a rate of 75revolution-per-minute (RPM). The filter may be temperature controlled towithin 1° K. The FPA sensor produces a single video of 14-bit words at60 Hz. The words from a contiguous region of the focal plane aretypically combined to provide a subtended limb viewing area typically250 km wide by 4 km high.

The limb sounding sensor of the present invention thereby provides goodozone profiles at an affordable cost and at a low weight. In particular,the limb sensor embodiment includes provisions for on-board calibration,signal processing of the FPA output and steering of the field of view toobtain 100% earth coverage.

Having thus described several particular embodiments of the invention,various alterations, modifications, and improvements will readily occurto those skilled in the art. Such alterations, modifications, andimprovements are intended to be part of this disclosure, and areintended to be within the spirit and scope of the invention.Accordingly, the foregoing description is by way of example only and islimited only as defined in the following claims and the equivalentsthereto.

1. A microbridge detector, comprising: a semiconductor substrate; amicrobridge disposed above the semiconductor substrate, the microbridgecomprising an active area and a pixel collection area, the pixelcollection area being an area of the microbridge that receives energythat is conveyed to the active area, wherein the microbridge detector isconstructed and arranged such that, for incident IR radiation normal tothe microbridge, the active area is smaller than the pixel collectionarea; downwardly extending leg portions which are a continuation of themicrobridge and which support the microbridge above the semiconductorsubstrate so that a thermal isolation gap exists between the microbridgeand the semiconductor substrate; and electrically conductive pathsincluded within said downwardly extending leg portions connecting theactive area to the semiconductor substrate.
 2. The microbridge detectorof claim 1, wherein the active area further comprises an infrared (IR)absorbing layer.
 3. The microbridge detector of claim 2, wherein theactive area is configured to absorb incident IR radiation and convertthe absorbed IR radiation into heat.
 4. The microbridge detector ofclaim 1, wherein the active area does not comprise an IR absorbinglayer.
 5. The microbridge detector of claim 1, wherein the active areais configured to change resistance in response to a change intemperature.
 6. The microbridge detector of claim 1, further comprisinga reflector, disposed between the active area and the substrate, thereflector being configured to reflect radiation towards the active areato enhance an absorption efficiency of the detector.
 7. The microbridgedetector of claim 1, wherein the active area is patterned withalternating absorption regions and transmissive windows.
 8. Themicrobridge detector of claim 1, wherein each of the pixel collectingarea and active area has a length, and wherein the length of the pixelcollecting area is greater than or equal to twice the length of theactive area.
 9. The microbridge detector of claim 1, wherein theelectrically conductive paths have a length such that a thermal timeconstant of the microbridge detector is substantially the same as thatof a microbridge detector having an active area substantially equal tothe pixel collection area of the microbridge detector.
 10. A microbridgedetector, comprising: a semiconductor substrate; a microbridge disposedabove the semiconductor substrate, the microbridge comprising an activearea and a pixel collection area, the pixel collection area being anarea of the microbridge that receives energy that is conveyed to theactive area, and wherein the microbridge detector is constructed andarranged such that, for incident IR radiation normal to the microbridge,the active area is smaller than the pixel collection area; downwardlyextending leg portions which are a continuation of the microbridge andwhich support the microbridge above the semiconductor substrate so thata thermal isolation gap exists between the microbridge and thesemiconductor substrate; and electrically conductive paths connectingthe active area to the semiconductor substrate.
 11. The microbridgedetector of claim 10, wherein the active area further comprises an IRabsorbing layer.
 12. The microbridge detector of claim 11, wherein theactive area is configured to absorb incident IR radiation and convertthe absorbed IR radiation into heat.
 13. The microbridge detector ofclaim 10, wherein the active area does not comprise an IR absorbinglayer.
 14. The microbridge detector of claim 10, wherein the active areais configured to change resistance in response to a change intemperature.
 15. A microbridge detector, comprising: a semiconductorsubstrate; a microbridge disposed above the semiconductor substrate, themicrobridge comprising an active area and a pixel collection area, thepixel collection area being an area of the microbridge that receivesenergy that is conveyed to the active area, and wherein the microbridgedetector is constructed and arranged such that, for incident IRradiation normal to the microbridge, the active area is smaller than thepixel collection area; downwardly extending leg portions which are acontinuation of the microbridge; and electrically conductive pathsincluded within said downwardly extending leg portions connecting theactive area to the semiconductor substrate.
 16. The microbridge detectorof claim 15, wherein the active area further comprises an IR absorbinglayer.
 17. The microbridge detector of claim 16, wherein the active areais configured to absorb incident IR radiation and convert the absorbedIR radiation into heat.
 18. The microbridge detector of claim 15,wherein the active area does not comprise an IR absorbing layer.
 19. Themicrobridge detector of claim 15, wherein the active area is configuredto change resistance in response to a change in temperature.